Can I use a Vista Replacement Disc as a secondary OS?

If I use a replacement disc with a 25 digit code that I've already used on another computer to be the 2nd OS on a MBP, will Microsoft's servers know? I'm positive that I can upgrade from this disc to Windows 7(and once I upgrade, I won't be flagged for using an invalid copy, almost as if the source Windows is lost), but I want to know if I can use the disc in the first place. I've heard of people saying they've never been notified by Microsoft, but I sort of need to buy the Windows 7 upgrade for $50 before July 11 when it goes back to $100 if I can indeed use the Replacement disc. Or do I just call Microsoft to deactivate the code on my PC laptop so I can use it on the MBP (am I then allowed to use Vista on my PC laptop after that?).