Just re-opened registration. I added Question and Answer verification. Hopefully that works as well as the upgraded (and presumably more secure) software.
I can't seem to upgrade to vBulletin 4.1 just yet.
vBulletin 3.6 and higher requires PHP 4.3.3 or greater and MySQL 4.0.16 or greater!
vBulletin 4.0 and higher requires PHP 5.2.0 or greater and MySQL 4.1.0 or greater
I don't have MySQL 4.1.0 or greater, though I do have PHP 5.2.0 or greater, I believe.