Please help!!!

I have a Powerbook G4 running OS X 10.5.8 and for some reason I can't get it to lanch apps or anything. The finder got corrupted and I've tried everything to get to disk utility but I can't. I tried safe mode. So I figured I might just make a partition on an external drive for my mac and lanch it off this copy of my HD I made a while back. It's in .hfs format. It used to be a .dmg but I was wondering since I (Sorta) don't have a restore disk if I could mount it to a mac partiontion launch my mac from that and fix the finder file. How can I do this? I also have a .iso I got online of the restore disk but I'm not sure it's the right one since they have .exe's on the disk. Not really complying with the info I used to remember about my disk. Please help.