found my answer
http://technet.microsoft.com/en-us/library/bb457053.aspx
XP 64 will support up to 16 GB. Now I know my next OS.
Geek Speak » in reply to does 64 bit xp see more than 4 GB of Ram?
http://technet.microsoft.com/en-us/library/bb457053.aspx
XP 64 will support up to 16 GB. Now I know my next OS.