PCI-e 2.0 is completely backwards compatible with any motherboard or video card combination, so you don't have to worry about which revision of PCI-e your motherboard or video card is.
If you have $250, I would shop around for a nVidia GeForce 8800GT. Those things have been blasting more expensive cards out of the water (8800GTS cards that came out the year before for $100 more), and is pretty much the best bang for your buck on the market.
A Dramatic Leap Forward--GeForce 8800 GT: It's A Whole New Ballgame Now VGA Charts 2007 | Tom's Hardware
Seriously, it would be almost stupid right not to not get a 8800GT.