Thanks very much for your reply, Bob23.
I tried that (I admit I may have done it wrong). I opened the file in mp3DirectCut, selected the entire file, executed Special>Auto Cue, set the interval for 5 minutes, and saved. When I played the resulting saved file it opened again as a single track, and the "Next Track" button was non-functional.
Maybe I wasn't specific enough with my question. What I want to do is to take one long file and, without having to separate it manually into individual 5-minute segments, insert track marks at 5-minute intervals so that I can use the "Next Track" and "Previous Track" buttons to move forward and backward in 5-minute increments while the file is playing. I don't even know if that's possible using this (or any other) tool, but if it is I can't figure out how to do it. I haven't even figured out what a cue sheet does yet.