FWIW: The active partition...there can be an active partition on each hard drive and the only reason for making a partition is so that it can be the boot drive or host an operating system. If you remove the O/S, the partition will continue to be active...to no purpose. I've seen this on my own dual-boot systems. By definition...any multiboot system can reflect multiple drives with an active partition.
But...Win 7 is a little different from XP regarding this designation, I don't recall that XP has/had a tool for making a partition active...actually, I didn't know that Win 7 has such a tool. Maybe it's done automatically when installing Windows but I don't ever recall using a specific Windows function to make a partition active.
See http://windows.microsoft.com/en-us/windows/mark-partition-active#1TC=windows-7 for MS explanation.
"Don't mark a partition as active if it doesn't contain the loader for an operating system. Doing so will cause your computer to stop working."
Seems to me that your situation stems from the fact that you only have one install of Windows...and you have an active partition on a drive not reflecting the O/S.
Seems that you can easily fix that, using the MS documentation.
Then...retry your install of whatever program.