OK, this works for installing any printer to an x64 Win 7 machine, where the printer is attached to an XP machine (and presumably other OS versions).
I have to credit Barkdust45 on howtogeek.com for the vast majority of it.
The only extra bit relates to the use of Windows Update. You can't seem to use the downloaded LaserJet INF file - but good news - there's a simple way around it. When you have the dialog box listing the printers, you can hit the Windows Update button, and it will refresh the list of supported printers, and the LaserJet 6P is on the list of HP printers. Installing it will take the driver from the Internet.
The secret is based on creating a local port on your machine, for a local printer, but using the network name of a shared printer on another machine.
If you later want to delete a port you create, you can click a printer in the Add a Device or Printer, dialog, then click Print Server Properties, and manage ports from there. (Amongst other ways of managing ports.)
Alas this doesn't help me with my brand spanking new Fuji Xerox DocuPrint FX C1190 colour laser. No drivers for Windows 7 for this yet, so I'll have to try and find a substitute. Funny the 10+ years old HP can be got to work. Marvellous machines.
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This is easier  at least for me and it worked. The shared printer is attached to a Win 7 x64 box and the XP is x86. Credit Jimbo45 at sevenfourms:
I’ve posted on this before but to share Printers attached to XP computers with either X-64 or X-32 versions of Windows 7 is SIMPLE. These instructions are for the Printer attached to the XP machine (but works in reverse as well).
(â€ÂStand alone†Network printers can be done slightly similarly BTW).
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 X-86 or x-64).
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 “Poodlefaking†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.
Simple
(For a “Network stand alone printerâ€Â) at 4) chose TCPIP port
and at 5) enter the IP address.
If the printer is on the Windows 7 machine and you want to print on the XP machine then do the same instructions on the XP machine â€â€
port name in this case will be \\W7MACHINE\SHAREDPRINTER