Replacing the drive in its self won't work as it doesn't have the OS present on it. If your friend still has the grey CD/DVD's that the system came with you should be able to install a fresh copy of the OS on the mini.
Now I've got some bad news! The highest version this system can run is OS-X Leopard (10.5.8) and the apps need to be the older PowerPC versions.
Replacing the drive in its self won't work as it doesn't have the OS present on it. If your friend still has the grey CD/DVD's that the system came with you should be able to install a fresh copy of the OS on the mini.
Now I've got some bad news! The highest version this system can run is OS-X Leopard (10.5.8) and the apps need to be the older PowerPC versions.