Lets look at this logically
You installed XP, most likely on the first partition on the drive. You then install Windows 8 Pre-whatever, most likely on the second partition.
You then overwrote XP, hopefully, which would have been on the first partition. For all I know, you may have installed Windows 8 Pro on the last partition.
But in Device Manager,
System is where the boot files are, and must be active. The
Boot partition is where the OS files are and the partition you have booted into. If you boot in to one version of Windows 8, it will say C: and the other, something else. If you boot into the other one, it will say C: and the original C: will no longer be that.
As has been mentioned, using the Winkey + Pause will bring up the System dialog, which will show what the OS is. Also, the Pre-releases showed the Build number in the bottom right, whereas a activated Windows 8 Pro install does not show a build number. The final release has a nicer cover screen prior to login.
And finally, you cannot just delete the first partition, no matter what OS in there. You could move the boot files, but you will have to know where you want to move them.