I have one Windows XP 32-bit PC still on my home network, with a HP LJ 4050 connected to a 64-bit Win 7 Pro PC.
I certainly don't have to set up a raw IP port to print from XP to the Win 7 printer.
The key is to add the additional printer drivers for the XP clients to the printer shared on the Win 7 box. It is essential that the same printer driver name is used for both the Win 7 and XP clients (obviously not the same actual driver). So you can't add PCL 5 drivers for XP if you are using PS or PCL 6 drivers on the Win 7 host.
It is poorly documented, and poorly implemented, but then MS don't have much interest in supporting XP.
On top of this, you need to ensure that the user logged in to the XP PC has a valid account on the Win 7 PC to be able to print.
I find the easiest thing is to create a workgroup and make all PCs members of it, then create an account on each PC for each user - ensuring that the names are identical - and then ensure that passwords are kept in sync. This is all a bit of a pain, and is why domains are easier to manage for larger numbers of users - but that's a discussion for another day.
SD