Sharing Media Files Between Vista PC and XP Laptop

I have a desktop with Vista Business and a laptop running windows xp. I want
to share a folder of pictures that is located on the desktop computer. (And
vice versa) I go through the share folder routine. Both computers can see
each other. On the vista desktop I can access the laptop shared folders.
However the problem comes when I use the laptop (xp) and i click on the
windows vista desktop it asks for a user name and password. I dont know what
this is. It says to be in a format similar to an email address. How do I
access this folder? Or any folder for that matter (I tried putting a few
files in a public folder but had the same problem) Windows help doesnt have
an answer I can find.