Ad Place (Should I Add Community?)

I would suggest formatting your stylesheet, it is currently improper (div#id), messy and looks unprofessional.
As mentioned above, when you are assigning a class you DO NOT need to have a preleading DIV tag.

Code: (/style/style.css)

body {
margin:0px;
background-color:#d9d6c0;
font:normal 13px;
line-height:20px;
color:#000000;
}
a.discreet {
color:#666;
text-decoration:none;
}
a.discreet:hover {
text-decoration:underline;
color:#333;
}
a {
color:#409f00;
}
span.highlight {
background-color:#ff4;
}
#navbar {
background-color:#505050;
text-align:center;
color:#ccc;
font-size:16px;
padding:10px;
padding:1px 12px 2px 12px;
}
#navbar a:hover {
background-color:#4d4d4d;
color:#cfcfcf;
}
#intro {
margin:50px auto 40px auto;
width:540px;
}
#intro img#logo {
width:287px;
height:101px;
}
#middle {
background-color:#eee;
border-top:solid 1px #ddd;
border-bottom:solid 1px #ddd;
padding:30px 0px 30px 0px;
}
#middle h2 {
font-weight:normal;
width:515px;
padding:0px 2px 0px 28px;
margin:0px auto 10px auto;
font-size:25px;
color:#aaa;
letter-spacing:-1px;
}
#middle ul#work {
width:515px;
padding:0px 0px 0px 30px;
margin:0px auto 0px auto;
list-style-type:none;
}
#middle ul#work li {
display:inline;
}
#middle ul#work li img {
width:125px;
height:125px;
border:solid 4px #d7d7d7;
margin:15px 15px 0px 0px;
}
#tail {
margin:30px auto 30px auto;
width:540px;
}

#footer {
background-color:#505050;
text-align:center;
color:#cfcfcf;
font-size:14px;
padding-top:10px;
}

Your index page is pretty messy too, I would suggest formatting your code better.

Code: (BEFORE)

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<link rel="stylesheet" type="text/css" href="style/style.css">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
<title>Ad Place</title>
<div id="navbar">
<a href="index.php">Home</a>
<a href="page2.php">Publishers</a>
<a href="page3.php">Advertisers</a>

<a href="page4.php">About Us</a>
</div>
</head>
<body>
<div id="intro">
<img src="style/images/header.png" id="logo" alt="Ad Place"/><br/>
<h2>Welcome!</h2>
<p>
Welcome to Ad Place! We provide free information on what ad providers there are and what they will do for you! We hope this information will help you make the best of your site and make some money!
</p>
<p>
Please feel free to browse the site and check out all our different areas of the site. We hope the information provided is helpful!You can view my contact information below!
</p>
<h2>Contact</h2>

<p>
Email: greg.froning@bobhoil.com
</p>
</div>
<div id="middle">
<h2>Affiliates</h2>
<ul id="work">
<li><a href="http://bobhoil.com/"><img src="style/images/bobhoil.png" id="logo" alt="BobHoil.com!"/></a></li>
<li><a href="https://www.paypal.com/cgi-bin/webscr?cmd=_s-xclick&hosted_button_id=7042524"><img src="http://bobhoil.com/donatebuts/donate.png"/ alt="Donate"></a></li>
<li><a href="http://www.110mb.com/aff.php?un=bobhoil"><img src="style/images/110.png" id="logo" alt="110mb.com Free Hosting!"/></a></li>
</ul>
</div>

<div id="tail">



<script type="text/javascript">

</script>
<script type="text/javascript" src="http://www.projectwonderful.com/ad_display.js"></script>
<noscript><map name="admap38039" id="admap38039"><area href="http://www.projectwonderful.com/out_nojs.php?r=0&c=0&id=38039&type=6" shape="rect" coords="0,0,234,60" title="" alt="" target="_blank" /></map>
<table cellpadding="0" border="0" cellspacing="0" width="234" bgcolor="#ffffff"><tr><td><img src="http://www.projectwonderful.com/nojs.php?id=38039&type=6" width="234" height="60" usemap="#admap38039" border="0" alt="" /></td></tr><tr><td bgcolor="#ffffff" colspan="1"><center><a style="font-size:10px;color:#0000ff;text-decoration:none;line-height:1.2;font-weight:bold;font-family:Tahoma, verdana,arial,helvetica,sans-serif;text-transform: none;letter-spacing:normal;text-shadow:none;white-space:normal;word-spacing:normal;" href="http://www.projectwonderful.com/advertisehere.php?id=38039&type=6" target="_blank">Ads by Project Wonderful! Your ad here, right now: $0</a></center></td></tr><tr><td colspan=1 valign="top" width=234 bgcolor="#000000" style="height:3px;font-size:1px;padding:0px;max-height:3px;"></td></tr></table>
</noscript>

</div>
<div id="footer">
Copyright © 2008-2009  Ad Place   Site Created By: <a href="http://bobhoil.com/">BobHoil.com!</a>

</div>
</body>
</html>

Code: (AFTER)

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<link rel="stylesheet" type="text/css" href="style/style.css">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
<title>Ad Place</title>
<div id="navbar"><a href="index.php">Home</a><a href="page2.php">Publishers</a><a href="page3.php">Advertisers</a><a href="page4.php">About Us</a></div>
</head>
<body>
<div id="intro"> <img src="style/images/header.png" id="logo" alt="Ad Place"/><br/>
<h2>Welcome!</h2>
<p> Welcome to Ad Place! We provide free information on what ad providers there are and what they will do for you! We hope this information will help you make the best of your site and make some money! </p>
<p> Please feel free to browse the site and check out all our different areas of the site. We hope the information provided is helpful!You can view my contact information below! </p>
<h2>Contact</h2>
<p> Email: greg.froning@bobhoil.com </p>
</div>
<div id="middle">
<h2>Affiliates</h2>
<ul id="work">
<li><a href="http://bobhoil.com/"><img src="style/images/bobhoil.png" id="logo" alt="BobHoil.com!"/></a></li>
<li><a href="https://www.paypal.com/cgi-bin/webscr?cmd=_s-xclick&hosted_button_id=7042524"><img src="http://bobhoil.com/donatebuts/donate.png"/ alt="Donate"></a></li>
<li><a href="http://www.110mb.com/aff.php?un=bobhoil"><img src="style/images/110.png" id="logo" alt="110mb.com Free Hosting!"/></a></li>
</ul>
</div>
<div id="tail">


<script type="text/javascript">

</script>
<script type="text/javascript" src="http://www.projectwonderful.com/ad_display.js"></script>
<noscript>
<map name="admap38039" id="admap38039">
<area href="http://www.projectwonderful.com/out_nojs.php?r=0&c=0&id=38039&type=6" shape="rect" coords="0,0,234,60" title="" alt="" target="_blank" />
</map>
<table cellpadding="0" border="0" cellspacing="0" width="234" bgcolor="#ffffff">
<tr>
<td><img src="http://www.projectwonderful.com/nojs.php?id=38039&type=6" width="234" height="60" usemap="#admap38039" border="0" alt="" /></td>
</tr>
<tr>
<td bgcolor="#ffffff" colspan="1"><center>
<a style="font-size:10px;color:#0000ff;text-decoration:none;line-height:1.2;font-weight:bold;font-family:Tahoma, verdana,arial,helvetica,sans-serif;text-transform: none;letter-spacing:normal;text-shadow:none;white-space:normal;word-spacing:normal;" href="http://www.projectwonderful.com/advertisehere.php?id=38039&type=6" target="_blank">Ads by Project Wonderful! Your ad here, right now: $0</a>
</center></td>
</tr>
<tr>
<td colspan=1 valign="top" width=234 bgcolor="#000000" style="height:3px;font-size:1px;padding:0px;max-height:3px;"></td>
</tr>
</table>
</noscript>

</div>
<div id="footer"> Copyright © 2008-2009  Ad Place   Site Created By: <a href="http://bobhoil.com/">BobHoil.com!</a> </div>
</body>
</html>

You have numerous errors throughout your website (example below) but formatting is key.

About these errors, they render your webpage blank in lots of browsers (including IE -7)

You CANNOT place direct links, divs or anything not background information in your header.

Code: (YOUR HEADER)

<div id="navbar"><a href="index.php">Home</a><a href="page2.php">Publishers</a><a href="page3.php">Advertisers</a><a href="page4.php">About Us</a></div>

Header does not mean the top of your page, it means data that is loaded, all your content needs to be placed in-between <body> tags.