I have resolved this problem for myself - hopefully this will help others:
Assuming you have sorted out your networking and all that, check out
how your PC appears on the network and make sure you remember the exact name.
Also- assuming that you have downloaded the correct driver for Windows 7 for your printer
on your Windows 7 PC (64bit)
Go to the XP PC/Laptop armed either with the Instal disk for your printer - or download the XP
driver for your printer from the net.
When you set it up it should ask for you to select which port - select any for now.
Next go it no printer properties (Control panel, printers, .......)
Select new port.
Now to name it.
type in this sort of address (lets call your computer MyPC, and lets say you have a Canon Pixma printer iP4000)
type '\\MyPC\Canon Inkjet PIXMA iP4000' notice it has to be very exact, one small error and this won't work
~ check on your network on your PC to see exactly how the printer is named.
Don't forget to click on apply and Ok etc etc Make sure the tick box is now ticked as your default printer.
You may be required to reboot - I didn't have to on my setup
Next print a test page
It should work- unless you mistyped something
Good luck anyone who is battling with this problem