Create a new folder and move all three MP3 files to it. While the files are moving, hit the restart button. When your computer has rebooted, you will have one file in the folder!
However, I don't know the format of MP3 files. If they have headers (which is likely), then simply appending the start of one to the end of the next won't work. You'll end up with a corrupted file unified_file.mp3.
It's likely then you'll have to obtain an editor for MP3 files, open the first file, then paste in the other files one by one. I'm sure there's a freeware, shareware or Open Source version of one that you could use.
Name:
Anonymous2007-10-30 3:04
Search for a tool that can cut/append mp3 files that works on frame basis. Those can work with mp3s without decoding them first and reencoding them after.