Upgrade OSX issue:HELP

Hi all. I am new to the Mac Life, but am excited to learn. I just acquired a G5 PPC 2.0 gHz, 4 megs of RAM. It is running Tiger at the moment, but want to upgrade to 10.5 Leopard. I have a copy of Leopard that was given to me, but when I attempt to install, I am constantly asked to restart the computer to complete the install. I am not able to get past this. I have disconnected the internet, changed the password in admin. I am at a standstill. Can anyone walk me through the procedure for install? Thanks in advance.

Yea, don't use torrent software. There is zero quality control, could very well be trojaned, and is patently illegal in the first place. I suspect, this thread will be summarily closed.

Mike is correct. Don't use torrented software and that certainly applies to the OS. Just go purchase a copy for yourself.