Is there a way to make my monitor not auto-fit games?

[Doomish]

When I play any game such as HL2 or L4D (or even games like Bioshock that aren't Steam-run) and try to set it to widescreen mode, my monitor will auto-fit it to the screen, making it stretched and ugly. Is there a setting that keeps it from doing that? I have an HP L1706 LCD monitor if that helps.

It's fine if there isn't one, I can just play 1280x1024, but I was just wondering.

[Error_404]

Well there's your problem; why are you even trying to run in widescreen mode with a standard resolution monitor? If you managed to disable screen stretching, you'd be left with ugly black bars above and below your game. You might as well run them in windowed mode if you want to waste that space.
Generally most monitors don't have an option to disable screen stretching, so just run at your native resolution.

[Doomish]

Well, alright. I was mostly in it for the increased FOV that comes with widescreen modes to accommodate for the extra space, but that works too.

[Shadaez]

Most of the time it isn't a monitor thing, but a video card setting. Try the nVidia / ATI control center to make it keep aspect ratio. I used to use a 1280x1024 monitor in 1280x720.