down grading from xp pro to win me

hello, i had a comp specialist put in win xp for me previous to having windows me. when he was done he told me that i could no longer use my reboot disc that came with the puter as he wiped my system. i want to go back to win me but don’t know if i can becuase the guy told me i couldn’t. Is this true? If not, can i just put the old reboot back in and boot back to me?