My neighbor has an ancient 631CD that finally just died about a week ago. The only thing that he used it for anymore was to play cards and to surf the internet when they still had their 56k internet. I know its a mechanical error with the hard drive because when we boot the machine it goes to the OS and sit there and just loads. It'll sit there for quite possibly forever, but we turn it off after about 10 minutes. I was wondering if I was to put this hard drive in - ( http://welovemacs.com/ide500mb.html ) would I have to install the operating system on the hard drive again (I don't have the discs). Because of the fact that the hard drive I just showed was not in stock, if I were to put a larger one in, Ex: http://welovemacs.com/ide800mb.html would that work? Also, what operating system should I put onto this old mac? I'm a geared very heavily towards fixing PCs and I've never really worked on a mac before so if you could dumb everything down for me that'd be great. Thanks a lot for everyones help here.