I think no matter what Windows XP partition you're booted in, the OS will always identify itself as C: and label other proceeding partitions after it.
Boot into a Windows XP Partition. Go to Control Panel > Administrative Tools > Computer Management > Click Disk Management under Storage in the tree menu on the left...
Ignore the 'Personal File H:' in this example...the green outline is just showing that's it's an extended partition
Then on the right, the partition with the status shown as Healthy (System) is the currently active Windows partition. Hopefully, your disk reports as healthy . Take note of the drive letter.
Next, look below the table, and you should see a layout of your disks and their partitions. Locate that specific system partition marked with that drive letter. Whichever row it's on, is the Hard Drive which holds the system partition which you are booted into.
You can right click the specific Disk on the left, and click properties to find out what the drive model is.
you can have windows XP on a C drive and on a D, if you boot to windows on the Drive you will have a C drive there but your OS that your using will reside on the D drive, thus when you want to install programs on that one and not the other one you select lets say D:\Programs files\Office.
What you want to do is go into your Boot.ini file find the windows thats on the disk that you want to give a certian name to so you know when you boot up which one is which and on which partion your programs are on.
Deleting is simple, go into the windows partion you want and right click and format the partion you dont want that windows is on you can do this because the windows you are on isnt using the resources on the other partion.
*oh and i forgot to mention if you reinstalled windows sometimes you will see 2 windows to boot into in which case its just annoying and you can delete the false one in the boot.ini*