To be able to share files over the network you have to do 2 things:
1. enable file and printer sharing on both pcs
2. set at least one drive or folder for sharing
To set file and printer sharing, double-click on the network icon and select Properties. Click the box for sharing. Click OK
To share a drive or folder, open My Computer, go to the drive or folder you want to share, right-click on it and click Sharing and Security. Don't share the whole of your system drive.
You share a printer in a similar way.
Note that you do not have to set up any file sharing in order to access the internet.