In the first post of this topic you can see, what your computer should have:
Fifaplanet - Einzelnen Beitrag anzeigen - FIFA 11 - Technischer Support

CPU: Dual Core 2.4Ghz
RAM: 1 Gigabyte RAM (2 GB on Windows Vista / Windows 7)
DirectX® 9.0c

Your graphic card and CPU seem to be good enough. But what about your RAM?
Furthermore i don't know, wheather FIFA 11 is DirectX 11 compatible.