I know this is a little old and disregard if you already have it working, but I did this to load leopard onto my emac

take the hdd out and put it in another apple (or external whatever)

then make an image of your dvd with disk utility

Then using disk utility (iirc you have to do this from the boot cd) erase that hdd and make two partitions, make the first one the one you want your install directory to be and the next the one your dvd (atleast big enough for the install disc)

Then back to the diskutility on your computer restore the dvd to the partition you made for it after waiting a bit you should have it on their now throw it back in the mini and install from that to the first partition. I spose some things at the top could be done in a different order, but you get the idea.