Go to control panel. Open System Properties Select Advanced tab; Startup and Recovery; Settings button.
Select the Edit button and from notepad, backup boot.ini, by going to File; Save As and rename boot.ini. to something like boot.inibak.
Delete the line(s) referencing the boot option you want to remove.
Set timeout=0 so the system boots directly into Windows XP (you will not get the boot menu).
Save As boot.ini & Exit.
Now delete all the 64bit files on your D drive