copy OS to new hard drive?
copy my hard drive operating system to new hard drive?
Best to install a fresh copy using the OS installer, the. Use the migration tool to move your user accounts, apps & data over.
Do you still have the grey installer CD that came with the system? If not do you have the OS installer app on your HD presently?
Use a FireWire (or USB) external drive case to hold your new drive so you can install the OS onto it before you open your system.