Vista - wireless printing

Right i know there are loads of these thread things for wireless printing but i need to start from the beginning i have no network set up or anything.

I have a dell PC downstairs with XP connected by USB to a printer. This PC is connected to a wireless router by a wireless USB stick thing. My dell laptop upstairs has Vista on it and is connected wirelessly to the router. Where do i go from here i want to be able to print to the printer downstairs from up here.

if you need more info i will try and provide it, my knowledge is pretty limited.

thanks, jack