You can make a copy of it, put both copies in iTunes, hit get info on them, and change their start and end times.
For example, say you have a 30 minute song, but you want to break it into two songs that are 14 and 16 minutes long. You duplicate the file and import both into iTunes. You then set one copy to have the start time of 00:00 and the end time of 14:00. Then you set the other to have the times 14:00 and 30:00. If you need to break it into more than two parts, just make more copies of the original and adjust their start and end times accordingly.