Hi jobie2007,
I'm not a Mac user, so bear with me until a Mac user comes along

Try the tips here (not sure about what Java version you'd need to use for your ibook though).
Reduce the drag caused by LW

If you downloaded LW from www.limewire.com then there'll be no malware!

Use the forum search to look for slow computer, slow ibook g4, crashes ibook g4 or something like that...you might find some older threads to help.