As both Harddrives are running Vista, what is the purpose of a Duel boot system.
If you want to use it as a second master drive, you will need to format it as the BIOs and motherboard/ graphic drivers will be different and will cause a lot of problems (if it works at all)
If the resuced drive is an IDE drive (Wide grey cable), set it to Slave (jumpers at the back (where the plugs go), and it will usable as a data storage.
If it is a SATA drive, you will need to set the first drive to drive slot 1 and the rescued drive to drive slot 2.
You may also need to change the bios order.