The socket 754 is slated for sempron use, in the future, so it will become the lower end mobo. Not really a consideration, as agp graphics is being phased out, so you will want/need a new mobo to update your graphics in a couple of years anyhow. By then DDR2 might even be worthwhile.
The Ati cards run great on the Nforce chipset.
Saphire makes a lot of variations on each video card. If you have a model, check with the graphics forum. Those guys know thier cards.
Tell you right now though, stay away from the Atlantis R9800 with 128 bit bus. A 9600pro is faster.