The printer is connected to an XP computer which has been used successfully
with my other XP computer over the network. Windows 7 finds the printer on
the network when I try to add it but I then get the message 'driver not
found'
If I physically connect the windows 7 computer to the printer, printing works
fine.
In spite of what Mr Garcia said, you probably can't install a Windows 7
driver (especially a printer driver) on the XP machine until you
install Windows 7 on it
Also you don't really want to. The problem is one of networking; each
computer has to have its own *native* printer driver to create the
printer data stream, and networking gets the data to the computer that
is attached to the printer.
Since you can print OK on the Windows 7 machine when the printer is
connected directly, it sounds like you have to fix the network setup or
printer setup[1] on the Win 7 machine. You may also have to do
something different with the XP's network setup, but I would guess not.
Other than those generic remarks, I can offer no concrete ideas, since
I use my router to support my printer. It works very nicely and doesn't
require any other computer to be on, but it requires either a router
with a USB port or a printer with wired or wireless LAN capability
(mine uses wired LAN).
[1] You may have to go into the Win 7 printer setup and inform it
properly that you're printing over the network. Especially if you can
print directly to the printer without making any changes to the setup.
That implies no network setup is in place.