I can do that with my 8800GT!! A 4850 will be plenty for 1280x1024. If you want more power (not needed though) get the 4870. A GTX280 will be totally wasted as will crossfire.
At last, someone actually reading the thread. I can't believe how many people have read the resolution of 1280x1024 and still advise on the X2 4870 and GTX 280. The mind boggles as that would be a total waste of a graphics card. If the 8800GT can handle 1280x1024 with all the bells and whistles on then why are people suggesting cards that will be CPU limited unless you're hitting 4Ghz (roughly) and if one 4870 , even 4850 would be more than enough then what use would a second 4850/70 be or even the GTX 280?.