Open Audacity. Load the large audio file into Audacity. Save the file. Note where you save the file on your computer.
Determine the number of small files you want to create from the large file. Divide the total file length into the number of segments you want.
Highlight the Selection Tool. Drag the cursor left to right across the file timeline to select the amount of time you want for the first file segment. Select "File/Export Selection" from the drop-down menu. Export the selection as an "aiff" (MAC) or "wav" (PC) file type and note where you save it on your computer. Repeat with the remaining number of segments you determined from the large file. Close Audacity.
Open iTunes. Drag the first small "aiff" (MAC) or "wav" (PC) file into iTunes. Wait for the file to authenticate. Select "Advanced/Create MP3 Version." Repeat for each of the small "aiff" (MAC) or "wav" (PC) files. Note where the files are in the iTunes list.