@Ramhound: Mac OS X only requires a GPT partitioning scheme to INSTALL, it will boot from MBR if your copy the OS to such a disk.
@John: The simple answer is no, you can't. Here's why.
You should not convert a Windows installation in place, you should instead install from scratch. This is one of those problems where you would spend more time making copies of your data, and technical massages of the machine to get it to do what you want than simply reinstalling.
Windows does not care about not boot disks, so you can make your secondary disk into a GPT disk if you want to. You would have to do this if you had a 3TB drive anyway. Now, there are no easy tools to convert in place, you would be wiping the drive clean to change to GPT. (Remember, GPT and MBR are the underlying structure of the partitioning scheme, so by changing them, you are wiping the partition table clean.
Now, you were not clear on your usage of Hyper-V, is your system installed on top of Hyper-v? If so, then the answers change, because your system can be "copied", reinstall Hyper-V onto the GPT disk, then "copy" the system back, and you don't go through the reinstall process.
This is not how most people use there computer, but you mentioning these system makes this a possibility.
Sorry I can't be more positive.