Ok this is the question about windows 7, nfs mw, gta vc, and grapics card and its drivers? please help me.?

when i was using xp all the games were working well. I installed windows 7 and i dont know whether graphics card's driver is installed. when i tried to launch nfs mw it says speed.exe has stopped working and gta vc says no enough video memory. but they played well in xp. so i think my system meets requirements. I thought its the problem of directx but it's the part of win 7 now. In dxdiag>display directx features were not available and device name: standard vga graphics adapter and approx. total memory was not available. what's the actual problem. please help me. i've tried many things. Pls. It's been a headache to me.