From that time period it is either 1.1 or 2.0 and they are forward and backward compatible. Anything beyond 2.0 can require a bios update for support (like 2.1). I would get an inexpensive PCIe 2.0 card, anything newer and faster would be severely bottlenecked by the rest of your system anyway.
Also, insure that you have the latest bios version for your board.