There's minimum requirements somewhere, but an 8800GTS is actually a very good card, it will run with Windows 7 just fine. It is also DirectX 10 capable so you'll actaully see a slight improvement in the visuals and/or possibly a speed increase in supported games. This might be offset though in the slightly heftier (though not by much) processing cost of running Windows 7 compared to XP.
As for your motherboard, dxdiag might show the model number which you can lookup on the internet. Otherwise, model numbers are always printed in large print on the motherboard itself somewhere. Often by the PCI-e slots.
If you find a good excuse to upgrade your card, 8800GTS is going to be PCI-e, and so your mobo can run any PCI-e graphics card currently being released.