The same thing happens to me. I have been using my MacBook Pro for two years. Suddenly, about a month ago Limewire started crashing at startup after the first question about upgrading. Last week, I upgraded to Leopard, but nothing changed. My exception error is slightly different. It is as follows:

Process: LimeWire [3631]
Path: /Applications/LimeWire/LimeWire.app/Contents/MacOS/LimeWire
Identifier: com.limegroup.gnutella
Version: 4.14.12 (LimeWire 4.14.12)
Code Type: X86 (Native)
Parent Process: launchd [210]

Date/Time: 2008-01-07 10:54:59.220 -0600
OS Version: Mac OS X 10.5.1 (9B18)
Report Version: 6

Exception Type: EXC_BAD_ACCESS (SIGBUS)
Exception Codes: KERN_PROTECTION_FAILURE at 0x0000000000000000
Crashed Thread: 0

Application Specific Information:

Java information:
Version: Java HotSpot(TM) Client VM (1.5.0_13-119 mixed mode, sharing)
Virtual Machine version: Java HotSpot(TM) Client VM (1.5.0_13-119) for macosx-x86, built on Sep 28 2007 23:59:21 by root with gcc 4.0.1 (Apple Inc. build 5465)
Exception type: Bus Error (0xa) at pc=0x005b6dd8

Just started working again!

I reinstalled the new version of Missing Sync and after that, Limewire seemed to be okay. I don't think it's connected, but then again, you never know. Missing stopped working properly because I was using the Tiger version. They released the new version and after the download, it started up.

Strange.

I was in Leopard to start off with.

That's good you've got it working. However, I don't see the relevance. I think you've run into a lucky coincidence, or perhaps Missing Sync is packed with something that helped your situation. After all, our errors were slightly different. Yours indicated a Java process. Mine only talks about Limewire as the process. I have never used Missing Sync, and I have no need for it. So, I think I'm looking for a different solution. Congrats on yours, though.