It could have been a few things that mucked it up. It's usually Java updates. So the answer is to downld the "Offline" java installer & reinstall it. But if you updated quicktime, then see
QuickTime 7.0.4 bug stops LimeWire from opening!
BTW if you're now using Tiger, I'd highly recommend updating to Java 1.5 but you'll need to force LW to use it. See
http://docs.info.apple.com/article.html?artnum=301073
I also upgraded to Tiger & after updating to Java 1.5 noticed particular improvements in LW. This might have been more noticeable on my system however.