install Lion on Imac with macbook-pro HDD copy
Method #1

Do you have a Snow Leopard DVD? Install it on the iMac, make the Software Update, Download Lion from the App Store, Install it. Then boot the MacBook in Target Disk Mode and use Migration Assistant to import your Data to the iMac.

Method #2 (if iMac is capable of Mountain Lion => if not, use MLPostFactor)

Download Mountain Lion on the MacBook via App Store, boot the iMac in Target Disk Mode and install it this way from the MacBook. After Install worked, use Migration Assistant.