Windows XP 64-bit Edition is not compatible with Google Calendar Sync at this time
Calendar sync works in XP 64 using compatibility mode 
Well it does work for me – two way sync with Outlook 2007!
Simply save the installer to your machine, right click on the installer executable and select properties in the second tab Compatibility check the checkbox “Run this program in compatibility mode for: Windows XP.
Run the installer
Then before running the program, navigate to the installed executable with windows explorer. It will probably be in: C:\Program Files x86\Google\Google Calendar Sync\ right click on GoogleCalendarSync.exe and do the same as for the installer. Compatibility with Windows XP
run the sync…
via Windows XP 64-bit Edition is not compatible with Google Calendar Sync at this time – Calendar Help.