Games are not rendering at their full resolution

Hey. I recently upgraded to Windows 7 Ultimate x86 and I'm not regretting it in the least—the OS is amazing. However, I have been experiencing an issue when gaming.

I run a dual monitor setup with one being a Samsung 2253LW and the other being an HP vs17—their native resolutions are 1680x1050 and 1280x1024. On XP, all games ran in windowed mode at my Samsung's native resolution just fine. The vs17 would have conversation windows open and such while the widescreen held the game at full resolution, keeping the borders off the screen as much as possible.

After upgrading, most games no longer run like this without error. The resolution of 1680x1050 is perfectly selectable, but they're a few dozen pixels off height wise and the mouse cursor is rendered a few pixels below where it actually is.

I've tried a number of things, such as running with the basic theme, trying all compatibility options, reinstalling and uninstalling drivers, et cetera. The games are displayed fine when running at a windowed resolution which isn't my native one.

Any ideas?

Here's one example. You can see the window border at the bottom—the other three sides of it have been moved just out of view.

Here's another. The border is larger this time for some reason. Sometimes in this game, the bottom few pixels or so get 'stuck' and render a frozen image from the menu throughout gameplay, causing the resolution to shrink even more.

EDIT: Sorry, I somehow managed to post this in the wrong section. I meant to post it in gaming. Can a moderator please move it?

I see from your specs that you built your own machine, so my first suggestion would be for you to make sure you have installed all the latest drivers for your HD4850 - Drivers & Support | GAME.AMD.COM

It probably wouldn't hurt to make sure all of your chipset drivers are up to speed with W7 as well.