Resolved trouble setting up a dual boot system

I did post this on the XP section as well as it involves both Win7 & XP. Excuse me if it is redundant.
The situation is a little complicated (to me that is). Have Windows 7 installed on the C drive partition of a large (1 TB) HD. On the other D partition is Win XP. The problem is that the people who built the computer used a bogus copy of XP to set it up. I have a real one and want to replace the bogus one. I thought I could change the boot order in the BIOS and have the computer boot to the MSFT XP disc. But after I change the boot order to the DVD drive it still boots to the screen with the choice of Windows 7 or XP. If I choose XP, I am in WinXP and can't get the CD to overwrite the bogus XP. I do not want to chance anything happening to my Windows 7 installation as it's perfect and has a lot of work in building all the programs etc.
Any advice or direction to look into would be appreciated.

 

setting up dual boot

I tried the good code from my good disc and it didn't work as did calling MSFT, which also failed, I realize that because the codes don't match, that wouldn't/didn't work. The disc is clean as is the drive. The XP message was to delete the existing XP and then boot to a good cd. So far haven't got the cd to boot but still trying ideas.

 

Please explain the bold above, is it a good (ie original) CD? what problems are you having when booting from it.

 

The good XP cd does open but it would not overwrite the existing bogus XP already in the system.
However, I see a way to accomplish the fix but have a question. It seems the reason my XP good disc can't simply overwrite the existing bogus XP is that it is an earlier older version. It asks me to delete the new one and then reinstall my good one. That's fine by me, but I have a question. Is there a simple uninstall for Windows XP?
Reinstalling I know how to do but wondered if I can reinstall to a partition of my choice that happens to be on the same disc with Win 7 on a different partition? Any advice now is helpful as this seems like the easiest way.

 

Did the image of win7 partition last night -- great minds thinking the same. The details you have sent will be most useful. I tried to uninstall xp through control panel but xp was not in the list. Tried computer mgmt and tried to format the partition with xp but got a no can do message. Those methods would have been the easiest way and then reload using your advice the good XP. Can't do anything with the xp partition and can't overwrite with the cd because the cd is an older version. Frustrating. Any final thoughts?

 

Everything is working fine now.
Win 7 disk works much better than 3 rd party partition programs, which caused some of the problems. Even though conceptually, working on a partition that did not have the OS on it, should have left the other partition fine, afterwards the C drive would not work correctly "currupted partition ".
I tried a few of the suggested programs and in the end BCD worked and the one that did the partition job cleanly was...surprise, Windows 7 disk.
Having backed up anything important saved the day as usual. I would make it mandatory (if that were possible) that everyone make frequent images of their C drive and did backups.
All input was helpful and appreciated.
Best
Gary