Thanks for getting back, here's some details about the system I'm using. If you need more info please ask, like I said I don't know my mac very well yet!

Memory 160MB
Processor 500MHz PowerPC G3
OSX V. 10.2

I also noticed the hard disk seems to be partitioned, with two disk icons on the desk top - one OSX and one OS 9. The OSX hard disk is near full (200-300 MB left I think), the OS 9 disk has 3 GB and is hardly ever used (can I still use this part of the disk in OSX?). I was thinking the lack of memory may be causing probs? Ideally I think I'd like to wipe the hard disk and re install but not brave enough, having never had a mac before...plus its my girlfriend's computer...

Definitely downloaded from www.limewire.com, so no problem there, although after a couple of abortive install attempts I wasn't able to download limewire at all, getting the message "cannot create file" when I tried. The file seems to have downloaded fine now though...

Gonna try the safeboot/repair permissions now, thanks for the help.