Helping people with computers... one answer at a time.
While moving Windows from one hard drive to another is theoretically possible, it's likely to have issues and is not recommended.
I added a larger hard drive to my PC (now I have 2). I also upgraded from XP Home to XP Pro. But the Home is on the original drive and the Pro is on the new drive. I don't know how this happened this way. Is there anyway to get the Pro version off the new drive and over to the original drive without having to reformat the drives?
My first concern would be why the situation arose in the first place. There are approaches to moving the operating system, but my advice is not to.
When you add a hard drive, it's usually designated in the BIOS as primary or secondary. Primary is of course, the boot drive, and is where Windows expects to be installed. Typically when you install a second drive it will be the secondary, and not participate in the boot process at all.
If your new drive had been installed as primary by mistake, I would have expected your first reboot thereafter to fail, because the new drive would not have an operating system on it. Unless, perhaps, your BIOS is smart enough to check all drives.
When you install Windows, it will also present you with an opportunity to upgrade in existing installation or set up a new one. In the latter case, you could certainly have selected the new drive.
But the bottom line is that why it installed on the new drive may impact the success of the suggestions to follow.
Moving an existing installation of Windows is theoretically possible, but I would consider it risky. I'd expect it would be easy for many things to go wrong, putting you back where you started, or worse.
So the ultimate answer to your question is no, I would not recommend attempting to move the operating system.
In your shoes I would try one thing: swapping the hard drives. I started by pointing out that the drives are primary and secondary, and it's apparently installed the new operating system on the wrong drive. Make that drive the primary, and see if that results in what you want. Exactly how to do this will vary on your motherboard, your bios, and your drive types. And ultimately, it may not work. Depending on the exact configuration you ended up with, I can think of several issues that might invalidate this attempt.
That brings me to what I'd expect to be required: reinstall. Or rather, re-upgrade, making sure that the upgrade happens to the drive you expect. I might even go so far as to remove the second drive, perform the upgrade, make sure it's all working and then re-install the new drive, and make sure that you're still booting form the old one with the properly upgraded operating system.