Hi, I just tried Vanilla on localhost (Apache 1.3.27, PHP 5.0.5, WinXP) and it just gives me lot of error messages similar to this:
Warning: session_start() [function.session-start]: open(e:\PHP\sessiondata\sess_48a2dc41ea5226355fcaa67ccc6fd778, O_RDWR) failed: No such file or directory (2) in f:\offline\mysite\vforum\library\Vanilla.Session.class.php on line 63
looks like an issue with your php install. I'm not sure if it's possible to compile php without session support, but if it is it looks like you have. Or possibly a permissions issue.