Dual Boot - both Win 7

I'm a Beta Tester for a major audio program, so I need to have a copy of Win7 running on a separate partition so I can always go back to the stable version of my software in case the Beta version craps out.
I created an image of my C drive with Macrium Reflect, created a partition on another drive (calling it P), then restored the image to the P drive. Set up a dual boot... everything's cool.
I can boot to the P drive copy just fine. That drive shows the little Windows icon on it ... system is running from there.
Now, here's the issue. What I need to do is to uninstall the older version of this audio program in that version of Win7 (on P), leaving it intact on my original boot (C). Then I will install the new, BETA version under the P boot. This way I can boot to P for testing and boot to C for stable work.
I just ran some tests and have found that uninstalling programs while booted to P does not work properly... when I look at the drives side by side, I find that while the uninstaller for, say, Photoshop, went through it's process, it actually deleted the files from the C drive.
I assume that all file references in the P copy are still to files on the C drive.
Any ideas?
Thanks
Russell

My question here would be that when you boot up to the Windows 7 Installation on P:, what drive is shown as the System Drive in "Computer". Particularly, which drive has the little Windows flag indicating it is the system drive?

They both say "System", but the P drive has the Windows logo on it.

I just went ahead and installed from the discs... takes longer, but gives you a clean copy on a separate partition that knows where it is.
Cheers
Russell

no, i didn't change the drive letter of the C drive,
I created a new partition on another clean drive and called it P.
I made an image of C, then restored it to P.

What I have done now that does seem to work is this:
I ran the Win7 installer and when asked which drive to install to, I chose P.
It installed fine and now I can boot to either the new clean copy of Windows, or to the original copy that's still on C.
Cheers
Russell

a-ha
now I see what you're saying
So forgive me if this is a dumb question, but how do I change P to C.
I know you change drive letters in Computer Management, but if I boot to the volume on P, then try to change C to something else so I can change P to C, it won't let me do it.
Thanks for all the help
Cheers
Russell

Main install - C.JPG
disk management - P install.JPG
computer - P install.JPG