I'm currently using a Dazzle DVD Recorder with a copy of Studio 11 and when I'm capturing footage from my Xbox it seems to cut the bottom 6th of the screen from the capture.
I'm pretty new to the whole video capture/editing thing so I was just wondering if there was an easy solution to my problem.

Hmm, that's a bit specific, you may want to try on an XBox related forum as I doubt most people here would have any experience of grabbing from XBox.

The only thing that immediately springs to mind is this:

What resolution is the XBox outputting? Are you talking XBox or XBox 360?

If greater than SD (eg 720i or 720p) then this may explain it - maybe the dazzle device does not support HD?