001 Joiner is a little application with a simple interface that can Split and Join files.

The files have the extensions of *.001,*.002,*.003 etc.
A basic file might be something like Myfile.mpeg.001 and have more like Myfile.mpeg.002 etc. All you have to do is double click the file with extension .001 and the rest will be loaded into 001 Joiner.

From here you can Join these files together, either click the Join button and the file is Joined in the same Folder as the Split parts, or click Batch which will create a Batch file in the same Folder.

Then just double click the Batch file to Join the parts. You can also spilt files into various sizes from the program or from the right click in Windows Explorer.