Hi there!
I have exactly the same problem as dford!
My WinXP Pro SP2 stops just right before the 'Welcome' screen.
It just displays a blue screen (not BSOD!) with the Win XP logo on it. I can use the mouse arrow (but nothing to click?!?!), but I can't CTRL+ALT+DEL or anything!
Even with safe mode the error occurs.
And even with 'Last Known Good Config'
Before heading to a repair install over my previous one, I will wait for some feedback on this because I guess this is a rare problem... (I've searched the net and dford's post was the closest/similar description I've seen to my problem...)
On XP install I had only the necessary services, Sygate Firewall and spybot updated and AntiVir software updated....
With a rescue CD I have, I can access eventlog, but I can't find anything helpful or any hint in it...
Any clues?