I can't see any reason why it shouldn't work.
Dell Optiplex 760 USFF would have been tested for x64 as they sold it with downgrade rights for those who didn't want Vista. It looks like you also have all the x64 drivers you need available for download.
Just to clarify for others who read this, it's not "Windows XP 64-bit" - that was for Itanium processors only - but "Windows XP x64" which is short for "Windows XP Professional x64".