This newest version of Limewire will not start on my Mac. It crashes. I had the pro version but don't use it enough to justify continuing to pay for it, so I was going to revert back to the free version. Might Limewire be crashing simply because the subscription expired? Is there a known issue with Limewire and the Macs or perhaps with the latest update of Mac OSX?

Which Mac OSX are you using? Only 10.5 Leopard Intel 64-bit Only, 10.6 Snow Leopard 32 & 64-bit are compatible with most recent LW version.
When you say won't start, what happens when you attempt to open LW?

I'm using OSX 10.6.3 Snow Leopard on an iMac. What happens is that the program boots, the screen from which I normally would initiate a search appears , and then the Limewire window just shuts down and I get a message about it having crashed and to send a report to whoever receives such things.

The last time I used Limewire, which was before the most recent OSX update, Limewire ran just fine.

See Deleting LW Preferences folder in OSX. And after you open LW set it not to open at system start. ie: LW preferences -> Advanced -> System .. and uncheck option for start up at system startup. This might be causing part of the problem.