No, there isn't a way to do an OS swap for Creative Suite products. Volume licenses from what I know, are reserved for Enterprise users. I am not sure as to why you got that option when you installed.
I am moving your post to the Download and Install forum to see if the experts there have an idea.
Preran
Thanks. You may cancel that move. I was in a Hell of my own making. In reading of others in similar problems, I saw the mention of needing to install from original media. My first installation was from a download of DW CS3. I had the original disk, as well, so I uninstalled DW, and then reinstalled from the disk. Presto! The serial number now works. Disappointed that I cannot convert the Mac license, but I can't have it all, now can I...