[*]Install both camstudio and it's lossless codec.
[*]In Camstudio, in the video settings choose the camstudio lossless codec. In the audio settings make sure it's set to record from the speakers.
[*]Choose the recording region. If you have the region set to "region", then after clicking record you click and drag to select the area of your screen to record. If you have it set on "fixed", then you click to center the recording box (and in the fixed window you set the size of the box in pixels).
[*]Record your game or whatever, when you stop it'll have you save the raw recording file (give it time to compress the audio).
[*]Add your video file(s).
[*]Change "Convert To" to "AVI".
[*]Change "Device Preset" to "Xvid Fullscreen" (or widescreen/anamorphic, whatever you recorded was).
[*]Change the "Output Folder" to whatever you want, or leave it at your documents.
[*]Click the "Convert" button at the top, and wait. Video conversion can take a long time. When it's done it'll say "press any key to continue", and when you do it'll close.
[*]Do whatever it is you want to do with the converted files. Import into a video editor, upload to youtube, whatever.
These settings will ensure the smoothest recording (as long as your computer's up to the task), but will give you a max recording time of about 50-80 minutes at once (depending on the recording resolution and a bunch of other factors).