I have had a look around, but I cannot find the tutorial.
First of all, place it on your computer somewhere. For example, either on your desktop or your profile (click 'START', and there should be a link with your user name. Open it and place the unrrbpe.exe there). Do not open unrrbpe.exe.
Place a .bpe file in the same place as the unrrbpe.exe.
Type unrrbpe xx.bpe yy.bpe
('xx' should be the name of the file. 'yy' is the name that you want the uncompressed file to have).
If it worked, there will be a second .bpe file. This is the uncompressed file.