The gray disks that ship with newly-purchased Macintosh computers are system-specific, meaning
they can only be installed on the Mac model they shipped with, listed on the front of the CDs/DVDs.
You cannot use the disk from your laptop to load OS X on your iMac for two reasons:
1) The disk, as mentioned above, is system-specific and will refuse to install on your iMac
2) It is a violation of the EULA for Mac OS X and is illegal (1 disk = 1 computer, that's it, with the exception of the "Family Pack" of Mac OS X)
I'm assuming they want me to buy leopard for my imac as well...
Yes, that's the point. They want you to purchase one copy of Leopard for
every Mac you wish to upgrade to Leopard. That's how they make money and stay in business and produce great products time after time.
Have two Macs that you want to put Leopard on? You must purchase
two retail copies of Leopard. Three Macs?
Three copies. And so on.
Apple does offer a discount for Macs located in the same household with the Leopard "Family Pack," which is sold at a discount and allows you to install one copy of Leopard on up to 5 machines at home.
BUT there has to be a way to make it work?!?!!
Nope, ain't gonna happen. You're going to need to purchase a retail version of Leopard if you want it on your iMac.