Microsoft never supplied an uninstaller.
However you are always able to boot up some tool like GPARTED (see google) to delete the partitions on the hard disk so your next boot with your XP CD can create a new partition to install to.
As to the 2 XPs. Did anyone tell you to google BOOT.INI ?
I have a Compaq Presario V2000 laptop with 512 mb ram memory that had Windows XP installed when I purchased it approximately 5 years ago. The computer locked up so I installed the XP recovery disc which installed a copy of XP on the laptop (two xps on laptop). With two XP's on the laptop, I couldn't use the computer as some of the programs were lost. I recently installed Windows Vista Home Premium on the laptop. It works but is very slow! I know that I can purchase more memory for it but was wanting to uninstall Vista and re-install XP without purchasing more memory.
How do I uninstall Vista and reinstall XP?