sharing WD My Book 250gb ext drive

Ok, I am stumped. I just upgraded to Vista Ultimate on my main PC and bought a Western Digital ext 250GB drive to share across my network. I can’t seem to get it to share to my Laptop (running xp via wireless) and I get an error when I try to access the drive from the laptop (it sees it) about that I don’t have permission to access it. I can’t figure out how to get the Vista System to set up a user profile for Network users so I can share this drive openly across my home network. Any ideas?