Shared Printer Password

My colleague has two WinXP machines and one PC running Vista Home. These are
all connected via a Netgear router and can all 'see' each other. A shared
printer is connected to the Vista PC and each of the WinXP machines can see
it. In order to print, they must supply a username and password (valid on
the Vista) PC and this allows them to connect and print. However, they have
to do this each time.

I have suggested that the usernames on the WinXP machines be set up as users
on the Vista PC so that they can authenticate themselves. Am I barking up
the wrong tree or is this the way forward for his query?

Thanks for any suggestions