This is the quickest way to compress files, just not the fastest.

If you want to compress a file called "CTF-MapName.unr" in the ../Maps directory then do this.

Copy the file to the ../System directory.

Click the Start button then go to Run. Type in CMD then hit enter.

Use the "cd" command to change directory to your ../UnrealTournament/System directory.
(Hints: cd .. this will allow you to go up one directory)

Once you are in the ../System directory then type this command

ucc compress CTF-MapName.unr

This will add a file called CTF-MapName.unr.uz to the system directory.

Alternatively, you can replace compress with decompress to reverse the action.