The Ultra setting requires that you install the DX11 patch.
For "true" Ultra, you will also need to install the HD textures
Installing the HD textures requires a minimum of 1024MiB of SGRAM, you have 1280.
Either way. Crysis 2 can be acquired on the cheap, and it's also a very well designed game. It's worth playing even if you have to turn the settings down a bit