Windows 7: setting up a dual boot Win7 & XP

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.

Tap the F8 key repeatedly at boot to get the one-time BIOS Boot Menu key, select CD drive to boot.

XP is on a CD so if you only have a DVD drive that is your problem.

I know how to get into the bios and change the boot order but because it's a dual boot system on one drive it doesn't react the same.
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.

installing two OS's on one partition is not recommended...

If Win XP is on partition 2,Reformat the partition.
Dual Boot Installation with Windows 7 and XP
SATA Drivers - Load in Windows XP Setup on Dual Boot
SATA Drivers - Slipstream into Windows XP CD

Use EasyBCD 2.0 in Win 7.
Download EasyBCD 2.0.2 - NeoSmart Technologies

A bit more reading.
BCDEDIT - How to Use
System Restore Points - Stop XP Dual Boot Delete - Vista Forums

Thanks for the BCD suggestion. I would like to reformat the XP partition and reload my good XP but it is not available to format. Get a no can do message. Also tried through control panel but no xp in list of programs to uninstall. Am reading up on BCD as maybe an answer. Any last thoughts are appreciated.

There is no uninstall option for operating systems (THEY ARENT APPS, THEY ARE THE PLATFORM APPS WORK FROM), copy any files you want to keep from the XP partition to the Windows 7 Partition and format it from a non windows enivronment (use a boot disk).

As far as I am aware DVD drives all read CD's aswell, I havent come across one that doesnt.

Thanks for the input. I now get why I have been failing. Boot from a non windows environment sounds like the easiest way to go. I guess not from the Win CD install disc but something else?? Not sure what that would be, but would like to know as simply formating that partition would solve everything for me.
FYI: I could boot from the Win XP cd but not reinstall due to the good xp disc is an older version of the xp the computer makers put on as the dual boot.

Boot from the XP CD, during setup choose the XP partition to delete, recreate and full format, or just full format.
windows_xp_installation_partit

XP will steal the boot from Windows 7, so follow the steps in Method two here to restore a Dual Boot Menu: Dual Boot Installation with Windows 7 and XP

If you run into problems, simply mark Windows 7 partition Active, boot the Windows 7 DVD or REpair CD to run Startup Repair up to 3 separate times with reboots until Windows 7 starts, then add XP from Windows 7 with EasyBCD 2.02.

Boot the XP, during setup select the partition where XP is installed and delete, recreate and full format, or just full format:


XP will steal the boot from Windows 7, so follow the steps in Method Two here to restore the Dual Boot: Dual Boot Installation with Windows 7 and XP

If there are problems, restore the boot to Windows 7 by marking it Active, booting the Windows 7 DVD or Repair CD to run Startup Repair up to 3 separate times with reboots until Windows 7 starts, then install EasyBCD 2.02 to add XP to Dual Boot. Partition - Mark as Active