You might want to read this before proceeding with a hard drive replacement. http://www.everymac.com/systems/apple/em...
In my experience this is the most difficult Mac to work on that is. Consider an external Firewire drive that will move to your next Mac and requires no installation. Your machine will need an ATA/IDE drive which are no longer made. Best Buy has a 250 GB at around $80. On the other hand you can get a 1TB external Firewire drive for $131. This is a nine year old machine and amortized out has cost you just over $100 per year to own. I wouldn't spend a great deal of money on it. http://www.amazon.com/Western-Digital-Fi...