i tryed it with a gtx280 on a 42" toshiba tv 1080p and had to run games and desktop at 1880 x 1036 for them to fit on the screen
That's because your HDTV does overscan which is what any HDTV that doesn't have native PC resolution support or DVI or VGA inputs will do. The overscan is there because when Sony and other manufacturers 1st created the widescreen DVD specs/resolutions they encountered problems with image edge distortion. Their solution was to just not display anywhere from 5-7% or the image edge. The problem is when you output windows or games via component or HDMI they will try to use all of resolution for the desktop, which will result in 10-15% of the desktop edges or image being offscreen. Luckily both Nvidia and ATI graphics cards allow for overscan compensation.
Both of you should be able to get a 1280x720 resolution or an overscan compensated 720p resolution . I only run an overscan compensated (1136x664) 720p on my PC as my HDTV only does 1080i -1920x1080 @ 30 fps- and I really like to be above 30 frames for racing and flight sims. Besides my gaming rig is too wimpy in the specs department to handle such a high resolution.

Satain, since your able to get a perfectly displayed 1080p I'd recommend trying 1280x720 if you want a lower resolution. If you have a DVI or VGA input on your HDTV you should always use it as that allow for the native PC resolutions - there's no advantage of connecting via component or HDMI.