For pieces and upgrade parts visit
iFixit: The free repair manual
I go there at times when my macbooks start acting up. I have fixed my personal macbook, a friend's iMac and my boss' macbook.
And they also have older mac hard drives, memory and upgrades.
I do agree with Scott that hard wire would be a real good way and cheap way to go as well. I would be a tad hesitant about bumping up to Leopard though. It's a bit lagging on the older non-intel macs. I would look for Tiger as your next upgrade. Someone has to have it either for free or less than 5 bucks.
Enjoy the Mac, that version wasn't bad at all just a bit slow for these days.
-Ray-