On mac osx it's not an issue so much. afaik osx allocates as much ram as required at the time. But also remember that all osx programs use virtual memory so you need to have lots of sufficient HDD space. There's ways of reducing ram usage but not until you get LW to open.

Also see this:http://www.limewire.com/english/content/support.shtml re: osx issues

So how much ram & spare HDD space do you have?