vB 3 Hacks are not yet allowed on this site. They will be allowed soon after RC1 is released of vBulletin 3.0
Most vB2.x hacks will NOT work on vB3, because most of the code has been changed completely. There are some minor, tiny hacks that may work on both versions, but I would NOT recommend trying it unless you're a fairly skilled coder.
RC1 will be released soon (how soon? nobody knows) and after that it'll probably be only a short while until vB3 hacks are allowed here. In the meantime, you can go to
www.vbulletin.nl for they have a fair few vBulletin
3 hacks already.