well, boot that up and click start>run and type in regedit
once that loads do a search for mklink and when it finds it right click the main folder on the left (for mklink) and export it, repeat this process until you have all of the entries.
Boot up into new system, make a backup of your registry and then double click the files you made, this will import them into your registry. You will need to go through each of the entries and update the filepath to be D:\ instead of C:\ (guessing on your drive letters, but just make it correct)
Then, it "should" work. It really depends on what os your coming from though. If its xp the reg entries can be VERY different, or exactly the same, so its a bit of trial and error which programs this works for.
Why cant you just re install it? If its because youve lost your code, then you might get away with backing up your folder, installing a new mklinks there and then restoring that folder (this will give you registry keys) but that would depend where it stores its licensing data.