Image does not fit the screen

Hi, I recently bought a new computer and instead of using a monitor I'm using my TV as the image output.

I'm not sure wether to post this in Hardware or software, but I don't think it makes a great deal of difference.

The image, for most games doesn't entirely fit the screen, its like that for most games such as GW itself and some source engine games however it is not like that for the desktop and UT3.
I lose about 1/5 of the screen if its too big, and about 1/5 when its too small.

My specs are as follows:

i7 920 @ 3.33ghz
Gtx 285, Palit 2gb version 700/1300/1594
6gb ddr3 @ 1381mhz (or something)
I'm running it on a 42inch tv, all games running at 1080p (it does support it) except the ones that don't fit the screen which are run a little bit smaller.
The tv is a toshiba regza something or other.

Any idea how to fix this?

*Edit: It is using HDMI also

s-video?

you'll want dvi/hdmi

do you have it on a Clone setup or TV only?

No, it is not a clone display. If I understand what you mean...
The TV is the primary display. The only display for that matter.