Hi Greg,
You may be able to 'clone' one of your working drives to the iMac. Cloning makes a full bootable copy of your drive, compared to just copying files. Make sure that the iMac will run OSX as some may not. If both computers have firewire, you can clone them by turning off iMac, connect with cable and starting the iMac in 'Target Disk' mode. 'Mac Help' discusses 'Target Disk Mode' and tells how to connect 2 machines.
This article lists some of the machines that can be connected, discusses how to connect 2 machines and goes over the process in some detail.
http://support.apple.com/kb/HT1661
You may be able to use 'Migration Assistant', in the OSX 'Utilities' folder or 'Carbon Copy Cloner' shareware, link below, to get OSX onto the iMac. I've used both with success depending on the specific machines, how they're set up and how they're connected.
http://www.bombich.com/
Important: Don't forget to backup critical files before doing any of this.
Have fun