It should work. With a quick search I've seen where that motherboard has had problems working with various gfx cards. Best I can tell you is go for it, worst case scenario it doesn't work and you have to return the card. Newegg is good about returns, I've had to do it more than once myself.
As for DX10 don't worry about it. IIRC DX10 won't run on XP but the card is fully capable of running with DX9, which your PC most likely has.
As for the 9800GT it is a good card. I've got 2 of the PNY 1gb ram version running in SLI on my desktop right now. Aside from the fact that they really need better cooling than what I can currently provide they work great.