I record my games in HD using CamStudio, which is a pretty small program. But in order to have the ability for HD you need to dowload the lossless codec for it. After you install it and start up the program you can select or type in your desired resolution (in CamStudio it's called "region"). To find the codec all you have to do is search "camstudio lossless codec" in google. I think there are different versions, and though they all do the same thing, you might want to get the latest. (Which is 1.4 at the moment.) Hope this helps.
EDIT: With CamStudio you have to start recording THEN open the game. If your going to edit/trim the video anyway than this shouldn't be a problem. But you might find Dark Goblin's method more useful.

(I didn't see it since I was in the middle of typing mine at the time.)
Cheers, Jake
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-The Clarkson Residence- (WIP)