Assume the computers are call XPMACHINE and W7MACHINE.
1) Ensure Printer on XP machine is shared - assume it's called SHAREDPRINTER.
2) On the Network Browsing on your Windows 7 machine ensure you can "See" the Printer share.
Now on the Windows 7 machine do the following (doesn't matter if it's x86 or x64).
3) Control Panel==> add LOCAL (Yes LOCAL) printer. I know it's on a Network but hold your horses -- what we are actually doing is fooling the Windows 7 machine into thinking it's running the printer.
4) Create NEW port==>Local port
5) Portname is \\XPMACHINE\SHAREDPRINTER
6) Now Windows 7 will load a driver and you'll be able to print on the XP machine
I.T. Tips from fergus.it