mp3splt is a really useful little tool to chop big mp3s into smaller ones. I use it mainly to split audio books into finer grained sections for easier navigation in the car or on my ipod.
To achieve this I use the following command
C:\Program Files (x86)\mp3splt>mp3splt d:\temp\audio\TheAdventureoftheBlueCarbun
cle.mp3 -a -t 30.00 -d d:\temp\audio\bluecarbuncle
This will split my mp3 file into 30 minute (-t 30.00) chunks, auto adjusting to cut in silent parts (-a) and writing the output files into a directory, creating if necessary.