From Pescados Software:
If you usually download movies, music or large archives from news groups, public web servers, streamload, edonkey or whatever place, this is your tool. If you'd like transportate a 5MB document in a floppy disk to your home, or fit a 400MB archive in two ZIP discs, or even move a 7GB film to a computer with a DVD burner and you only have a single CD-RW, this is your tool. If you wish share a 6MB document with your PC-friends over the internet and you can only put up online chunks of 1MB because of your ISP restrictions, this is your tool.
MacHacha will do a simple job: split archives into smaller parts and join them when requested.