Well, having gone 24 hours without sleep between fixing up my board and work, I thoughtr I should make the idiot's guide to all this, because I feel like quite the idiot. You'll hear a lot of people saying things like "just reupload the files" but that didn't work for me at all, so here's your ultra-simple step-by-step guide.
And remember, there are no stupid questions.
1. Download phpbb 2.0.11
2. Unzip it.
3. Open config.php and change the values for userdatabase, username, and userpassword to the values for your SQL. If you do not know the dbname, username, and password for your database you will need to ask your host for help in this matter.
PHP:
<?php
//
// phpBB 2.x auto-generated config file
// Do not change anything in this file!
//
$dbms = "mysql";
$dbhost = "localhost";
$dbname = "userdatabase";
$dbuser = "username";
$dbpasswd = "userpassword";
$table_prefix = "phpbb_";
define('PHPBB_INSTALLED', true);
?>
Not screwing up at this stage is important! Make sure there are no extra lines, because if there are you will end up completely lost until your more php-saavy friend says "Well no duh it doesn't work, you probably have an extra space above the first line of congif.php". And your friends showing you that you suck at the internet isn't good.
4. Delete the old directory entirely. You may want to backup your avatars, pips, and smilies first, because for security purposes it is much safer to delete this.
5. Upload the files for php 2.0.11 just like you did when you first made your board.
6. Run
https://www.yourdomain.com/yourphpbburl/install/update_to_php2011.php
If you can't figure out how to change that into your URL, you fail at life.
Or you need to let me know to explain that better.
7. At this point, if nothing has gone wrong and all your templates have also been replaced, it should work. If you are missing templates you'll need to go into the SQL and switch it to subSilver manually.