OK, well with the iMac in Target mode and the MBP in normal this is where I'd run Diskwarrior to repair the iMac's hard disk but I'm guessing you don't have Dsikwarrior ( an essential tool in my opinion).
Soooo with the iMac, visit Apple's site here
and download Onyx, install it, run it, and carry out the full maintenance routine. If you're very lucky it will repair the hard disk enough for it to mount on the MBP.
As a final option, how about booting the iMac as normal and putting the MBP in Target mode and mount it on the iMac. This should allow you to transfer the files between the two Macs.