You didn't say what your OS is but here goes:
WINDOWS XP
1. Click on the Start button, select Control Panel
2. Double-click on the Windows Firewall applet
3. Select the Exceptions tab
4. Check the box beside File and Printer Sharing
5. Click the OK button.
You have just enabled File and Printer sharing on Windows XP.
WINDOWS 2000
1. Click on the Start button, select Settings, then Control Panel
2. Double-click on the Network and Dial-up Connections applet
3. Right-click on your Local Area Connection and choose Properties
4. In the components listing, if you do not see File and Printer sharing
for Microsoft Networks, then you will have to install that component
from your Windows 2000 CD.
5. If it is present and not checked, then check it and click the OK button.
You have just enabled File and Printer sharing on Windows 2000.
Hope it all helps