As long as you're both on the same intranet, turn on Windows File Sharing for the particular folder or drive (with a right-click you can see the option). You'd need to setup a user on the PC who will have access to that folder/drive. Then, on the Mac, simply select "Connect to Server" from the "Go" menu. The PC will show up in the dialog. Double-click it, enter your username and password (that you set up on the PC), and you're in.
Don't bother setting up FileSharing on your Mac; it's not necessary as you're going into the PC.