nope, it is also compatible with panther. it is just that that tiger has G5 specific hm.. parts and therefore has to be freshly installed and not for example cloned. in any case he has an intel mac so everything has to be new. new os, new partition scheme....
also, it don't know whether this will work but have you tried connecting the macs with the firewire. Then booting the install dvd from the G4 and selecting the intel mac HD from the menu