Installed a new SATA drive in my friend's PC and trying to figure out how to set the old one as a secondary drive.

I removed the old one, formatted the new HDD and installed Win-7 and it's running great. I want to add the old one now so he can copy off all of his files to his new drive and use the old one as a backup, but I'm concerned there will be a conflict when I add a second HDD with an OS to the setup (I haven't tried it yet, but I know this used to be a problem with the IDE's if there were 2 Masters installed).

Is there a simple solution to my dilemma?