Can i play games that are Directx 9 using Directx10?

You can play either directX9 if you have directX10 card or in DirectX10 mode.

Like in crysis you can pick directx9 mode or 10.

You need Vista for directX10 also.

do you know about upgrading video memory?Jaiden114

You can't; The only way you can upgrade Video card memory is if you put in a better video card. Either that or you have onboard that takes from your system ram to make up for a short amount video ram and you just add more ram to your system (onboard isn't meant for gaming, so don't even think about this)