these days for 500 bucks, you can get a dual core 3ghz, with 3gb of ram for about 500 bucks. and you can find discount refurbished (was returned for a defect; ie, hard disk failed and was replaced, but system is otherwise new) systems for like $250.

now if the original poster is actually using a modern computer (2ghz+, 512mb ram+), i'd suggest checking for viruses and spyware.

also make sure other systems are fully updated. java especially, a number of versions back had a major bug in it that did something like you described, and until java was patched, i was starting to worry if i might have to ditch limewire. java patched, limewire didn't change, and suddenly it was all back to good.