Hi, I am no techie expert, but as far as understand you can't simply create a new start shortcut on a new drive and expect it to start.
I currently have two partitions on my hard drive both with windows XP on them one for gaming the other for movies and music etc., I have to re-boot between the two partitions in order to use applications on them.
Back to your problem I would think that you will need to download the game again and install it on your new drive, inserting a new serial (I believe you can request 4 or 5 serials with a digital download) during set up. Then you will be able to delete the game on your old drive (make sure you copy over your game settings folder)
Hope this helps