On, the host computer, make sure you have printer sharing properly set up.
Printer and File Sharing has to be correctly set up.
Make sure both computers are part of the same workgroup, such as HOME. It is recommended that you choose a unique name for your workgroup though.
Make sure the printer in the host computer is actually being shared.
Go into the printer properties, and under the sharing tab, make sure "share this printer" is checked.
In the client computer make sure its set to home network. Vista like to set up its firewall to the network detected, such as home, work and public.
A bi-directional print server would solve the problem. Unfortunately, they are rare, and expensive. The NSLU2 would do the trick, as it does in my case, but require true computer knowledge, like the kind you get when you finish you CS degree....