HELP ME!!!

I have installed Windows 7 Home on my imac through Bootcamp. Everything works fine (i suprised myself) except for there is a problem with the screen resolution. There is no option for 2560 x 1440. Everything appears a bit squashed.

Is there something I have not done that I was suppose to. I have gone to 'update driver' and it tells me all drivers are current.

Tried calling Microsoft but they couldnt help me as they dont provide support for Windows on Mac :(