I'm using HDMI from the NVIDIA to Witcher 2. There's a option to resize the screen in nvidia control panel but it only effects the desktop. Is there a way to resize the screen for the game?

Are you playing on an HDTV instead of Monitor?

Yep

Your TV should have a "native" option in the picture settings. At least mine does, as did my last TV. You need to use this when connecting a PC to a TV because PCs are not designed for overscan like DVD players and cable boxes are.

Maybe I'm misunderstanding, But open the game launcher, click on options, you can set the resolution in the options menu.

Is that what you meant?

Nor really. I think Stinging Velvet probably had it right, but maybe depends on the HDTV. I have Toshiba 42" and LG 42' and I believe both have the functions he referred to.