From what I've found it doesn't appear the MS Shutdown.exe supports a switch which will put the PC into hibernate, unless it's a secret switch somewhere?
However I'm managed to find this which doesn't need installing:AMP WinOFF
Will work from the command line with the -hibernate option.
If MS XP has no way of doing it then I'll use this.
Another free software which will do it is this but it needs installing:Quick Shutdown