A brilliant guy named bink has posted this solution. I've tried it and it works great! Go to the following link and download the free trial of MP3 Rage. It works on more than just MP3s!

http://www.macupdate.com/info.php/id/3847

Start up MP3 Rage. Choose a file of the same type as you want to correct (like .sit for a StuffIt document). Drop it onto the top button on the Rage console (which says "Display and Edit MP3 File Tags").

In the upper right-hand corner of the next window, you'll see the file name, then two windows labeled Type and Creator.

Write down the correct Type and Creator. Close the dialog box.
Drag the Limewire document onto the top button of the Rage console ("Display and Edit").

Change the Type and Creator boxes. (For StuffIt, Type is SIT5 and Creator is SIT!). Yes, use the exclamation point.

Click "Update". The dialog box says there are no tags in the file. Click the option "Delete Tags."

Voila! The file is fixed and will open with StuffIf like normal.
You can also use MP3 Rage to convert MP3s to AIFF for burning CDs!