Q:

Remote machine running XP won't shutdown, which processes should I kill and in what order? 

Unable to restart or shutdown remote Windows XP using psshutdown or psexec/shutdown.  I tried shutdown -s -t 0, but this failed.  Pulling the power isn't an option as no one at machine to do this. 
I'm still able to run tasklist and taskkill on the remote machine.  
Is it possible to trigger a fairly safe shutdown by killing processes?  

If so, which ones and in what order? 
If not, is there another way of performing a shutdown? 

A:

If you kill lsass.exe the machine will reboot, shutting down you have to execute a shutdown command.   shutdown -s -f -t 05    that will force a shutdown with a 5 second timer.