Not everyone can afford or just don't want to pay for MySQL activation... Although I HATE phpBB with a passion I guess I should help those with how to install phpBB3 on SQLite until SMF 2.0 comes out
Step 1:Download phpBB3 here:
http://www.phpbb.com/downloads/Step 2:Either unzip then upload or upload then unzip into your desired directory.
Step 3:Access your phpBB3 directory in your browser and click on the INSTALL Tab
Step 4:Click Proceed to next step button, then make sure all your files are writable if so Click Start Install.
Step 5:Where there is the database type selection box, choose SQLite... Now a little thing off to the side... make a file called SOMETHING.db now make sure this is a SUPER random name! I mean super random! like djskdjkijekh321398178w.db and upload it to a place not in the phpBB3 directory! (As phpBB3 wont allow it... Or for me at least), make sure to CHMOD the db to 777, then where it says Enter Database hostname or DSN put in the path to the .db file (So like /www/110mb.com/{YOUR_PATH}/htdocs/{PATH_TO.DB} Look in 110MBPanel for your htdocs path

) then hit Proceed to next step.
WARNING! It MUST be the path to the file! (EG: /www/110mb.com/{YOUR_STUFF}/htdocs/{TO_DB} or it WILL not WORK! Login to the 110MBPanel and in the sidebar click the link that says server and path info. Click it, and there will be your path to your htdocs
Step 6:If it says Test Successful, hit proceed again... then proceed with your installation as you would a MySQL installation

Easy wasn't it?
Now if you have .htaccess support put this in your .htaccess file the directory of you .db
<Files "{YOUR_DBNAME}.db">
Order Allow,Deny
Deny from All
</Files>
So there you have it =]
I'll say it here, SQLite has a huge downside (a couple)
1) Anyone can access your db file without proper pre-cautions you can either stop it or help the chance of no one getting to it.
- You can buy .htaccess support and do the .htaccess thing I showed...
- Or you can make the db file name super random...
- Rename your db file every so often. (Be sure to make changes in config.php file though too!)
2) It can be slow. After time and you getting more members, posts or whatever your database gets bigger and bigger. My default installation file was already ~576Kb

so imagine 100 posts and members running on that. The reason is, its nothing like MySQL. With MySQL it can go in and go right to a certain row, table column etc, and ignore the rest, as if it doesn't exist. Now with SQLite... its a different story. Every time something is loaded, it has to haul out your db file, find it and do whats needed. So the bigger it is the longer it takes for it to find something in it and get it out. So its not recommended with big communities.
DEMO:
http://northsalemcrew.net/phpBB3/Please feel free to register on the demo, post, or whatever you please to get the feel of it... (yes, it asks for email, but you dont have any activation thing

)