splitpea is a command-line tool written in Python that can split a file into multiple fixed-size pieces and join those pieces to form the original file.
splitpea runs on Linux and Windows using Python 1.5.x and above (although it's only been tested with 1.5.2 and 2.1.1). Most Linux distributions should come with a standard package for Python. You can also download Linux and Windows versions of Python from the Python website.