Sorry, I'm out on work trips frequently and am away from the forums at times.
Thanks Zylstra for letting them know about my periods of absence
Davva, here's what you need to do:
Go to your system preferences, and click on "sharing."
On the left hand side check the box that says "file sharing." It should then change to "file sharing: on" on the right hand side. It should also tell you how to get to your mac share via your vista computer (like by browsing or going to afp://IP.Address.Here)
You'll notice that you have the ability to choose what folders are shared from that menu as well. Click on the plus sign under "shared folders" to add more folders that are shared. By default the only one shared is your "public" folder.
You'll also notice on the right hand side that you can choose what abilities each user has (read, write, both).
Let me know if you get stuck.