Actually there are plenty of ways to go wrong with an ATI card. Their driver support is notoriously bad. You might get lucky and everything will work fine or you might have some hardware/software that ATI doesnt support. And ATI is the best out of the bargain brands you mentioned.
If you want the greatest shot at compatability stick with NVIDIA cards. Definately go AGP if you have the slot. If you dont have an AGP slot then you might consider putting together a new box before you waste money on a PCI card that has been obsolete for 2 years.