Windows XP x64

Ok, having a problem. So I have XP Pro SP2 installed on my machine, but I just got a copy from MSDN of Windowx XP Pro x64 Edition and wanted to install it, but on the Boot from CD option from DOS it doesn’t give me the option for x64 Edition … any ideas?

(my machine is a AMD 64 Dual Core X2 - just in case someone thinks I can’t run x64 Edition)