It's not the hard drive, it's more likely to be that you're running Leopard on 512 MB or RAM, which needs more RAM. Of course, there could be a deeper problem, such as bad RAM in general, but not having enough RAM will produce a lot of slowdowns and potentially lockups, but, once again, I can't rule out some other problem in this situation. The beep(s) would indicate bad RAM, so I'd have to go with the RAM... potentially both slots are actually failing... I dunno...