Fobotsco
When you say:
"this may be something to do with the different way in which XP treats hardware ports. My terminology may be a bit imprecise but I think in XP you create "Virtual" ports and then XP assigns these to "real" ports"...you're on the right track.
Have run into a similar problem with the exact same HP printer at work. Wouldn't work on the assigned port and while I can't remember all the details moving it from port 2 to port 1 solved the problem or vice-versa.
Definitely hardware related though... and no, we don't have a fix yet either.
Newark