Hmm. I also use a 500mHz G3, tho I have 640 RAM. I've never had Limewire do this (I also use 2.4.4). Try leaving it on long term again and see if the same thing happens. It could have been a fluke.

Limewire is a memory hog, however with the dynamically assigned memory in OS X this isn't the problem it was in OS 9.x.