OK--more info needed. Which OSX and LimeWire versions?
If it's just an OSX permissions problem, find your download folder on your hard drive, click once and see what "Get Info" says. You should show as the "owner," right?
btw--if you have just upgraded to OSX from (OS 9?), a Software Update/Safe Boot/Repair permissions is probably a good idea. The links for this are
here
cheers.