If you have a Leopard upgrade disc you will have to install Tiger first.
unfortunately, i already did the swap. does best buy or someplace like that sell an enclosure?
but yes, i have the 120gb drive that came in the computer, a 300gb external hard drive, and the new 320gb drive that i installed in the computer.
Someone will point you to some disk-cloning software whose name escapes me at the moment.
Just my two cents, but I highly recommend Carbon Copy Cloner (CCC). Simply clone your drive, using CCC, then install it in the computer and it should boot.
This way you have your original drive image, and the new one, so you can make sure it is all working before you reformat your OLD drive.
I would still recommend doing a backup before you use CCC just to be safe.
I used CCC when upgrading my drive in my laptop and it worked flawlessly!
Chris