Do you have 150 simultanous downloads? If not, next time it crashes, try looking at your processes:
by entering "ps aux" or "top" in your favourite terminal emulator. Maybe the JavaVM doesn't terminate correctly (if so, enter "killall java" or "kill -9 [number of process]).

Try restarting X, installing the newest JRE 1.4, rebooting your machine.

If all fails and LimeWire keeps crashing after just a few hours, send your IP and root password to gregorio@gmx.li, - I'll fix it for you. Yeah, you can trust me. Really. No kidding.