Eric, you can highlight the part you want to repeat, click on the "set loop to selection" thingie to the right of the times, then click the "loop on/off" thingie to the left of the times. The program will now play that part (and ONLY that part) over and over until you scream. This does NOT work if someone listens to it with a program other than Cakewalk - for instance if you save it as a MIDI and e-mail it to someone.

(To find the loop toolbar, click on Tools, Toolbars and make sure "Loop" has a check mark by it.)

If you only want a certain part to repeat, then have it go back to the beginning or another part, the only way I've found to do it is to simply copy and paste the repeated part in again.