Only tested on Windows XP. Save this as CapsLockToEscape.reg and merge it into the registry. Not responsible for any issues this causes.
Windows Registry Editor Version 5.00 # Remap CapsLock to Escape # 3a,00 is CapsLock # 01,00 is Escape # 02 = remapping 1 key. [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Keyboard Layout] "Scancode Map"=hex:00,00,00,00,00,00,00,00,02,00,00,00,01,00,3a,00,00,00,00,00