Reinstalling Windows XP OS after Windows Server 2003

Please help me solve this issue…
I have a computer that originally run on a Windows XP OS. However, due to a certain task I had on running some test of some software programs that our company is considering to install; I had to install Windows Server 2003 standard. After conclusion of the test, I wanted to reinstall windows XP. However, this was not already possible since I was unable to find the option of uninstalling windows 2003. I cannot also format my local disk C as I am denied permission. I tried reinstalling XP from the CD but this also failed as it went on for a short time before it displays “no supported upgrades found.”
