On your mac, open System Preferences, under "Internet and Wireless" click Sharing. Click the checkbox beside File Sharing. Click on Options in the right-pane and click "Share files and folders using SMB (Windows)" then make sure your username is checked.
Copy the files you would like to get to the PC into your Public folder (sitting in your Home folder.)
Now on your Windows PC, open "My Computer", click "Network" (or something along those lines, I do not have a copy of Vista around). You should see your Macbook listed in the list of computers on the network that will appear. Open your computer, go into "X's Public folder" (where X is your name) and the files will be there.
To move files from your PC to your mac using this, drop the files into the folder called "Drop Box."