bundled software cannot be installed - help?

having recently bought a flashy new macbook pro.. I'm hoping to sell my old imac (power pc G4 3.3) and make some money back (as much as it pains me to do so.. it's been a faithful friend). unfortunately I've misplaced the installation discs somewhere along the many moves I have done with it in tow so I bought some replacements from ebay. they are power mac G5 discs, but the seller promised it would work with G3, G4 and G5 macs. as soon as I rebooted with the first disc, it came up with the message 'bundled software cannot be installed on this computer'. as I had no idea what was causing this (I searched the internet.. and no luck) I opened the disk utility and wiped my HD thinking that this might help. it hasn't! I still get the same error message. I have emailed the guy who I bought the discs off and he's just pointed me towards apple discussions. should I be asking for a refund? was I stupid to think buying someone elses' installation discs would work and finally, will I have to buy a boxed version of panther/tiger for it to actually work? (I wish I had enough memory for leopard)