Awesome little program called VirtualDub! I use this pretty much every time I encode video.
http://www.virtualdub.com/
Load in a file, under video menu choose 'Direct Stream Copy' and under audio menu make sure it is also Direct Stream Copy (usually is by default). You might also change Audio Interleaving to 100 ms.
Click File, then 'Save Segmented Avi' choose the file size for each segment and boom, (after a short wait) you're done.
EDIT:
I also see you want it to be an mpg, well maybe you can re-encode it to that after you split the avi...?