Here's a tip that I found handy:

If you've got a clip that is pretty close to the length you need, you can go to "Effect", and "Change Speed." Make VERY SMALL changes, and hit undo if you mess up. (Ctrl+Z, for you computer studs out there).

This helped when I was trying to fit in a theme to the Batman game. I was shooting for a length of 30.222, and my track looped perfectly at a length of 30.268. I adjusted the speed SLIGHTLY...like, 0.070 percent faster. Audibly, it isn't different, but eventually I got to the 30.222 target.

(You can make slight adjustments if you don't nail it the first time...like keep adjusting again at 0.002 until you hit your target).

Hope this helps.

Pete