I installed WIN-XP on my itel based 15" MACBOOK-PRO using the built in Bootcamp program without any problem. I tried another more expensive program and it would not work. Does your I-mac have an itel processor? My understanding is that WIN will only work on a MAC with an Intel processor. I also upgraded my MacBook Pro to Snow leopard without a problem, and I use TMG7.4 all the time. I even use a USB microdrive to transfer my TMG saved db to my desktop Dell PC using WIN7 and my net book using WIN-XP.