When you have multiple machines running on a home network, it's easy to get into the habit of sharing folders indiscriminately, especially if you don't have a server to act as a file hub. This isn't a great thing to do on a laptop you regularly connect to other, less secure networks. Fortunately, you don't have to hunt around your hard drives looking for shared folders and disabling them one-by-one -- Windows provides a facility where you can view them all at once.
To view your system's shared folders, hit the Start button and in the "Search programs and files..." box type "mmc". The file "mmc.exe" should appear in the results list, so you can just double-click on it or press Enter to get it running.
This will open the Microsoft Management Console, where you can do quite a few tasks in the same application, but for now we want to use the "Shared Folders" add-in. Go to "File" -> "Add/Remove Snap-in..." and in the dialog that appears, find "Shared Folders" in the left-most list. Click the "Add >" button in the window's centre -- this will bring up another window, which you can just close by hitting "Finish". Finally, close the snap-ins window by clicking "OK".
Back in the main window, a node labelled "Shared Folders (Local)" will be visible in the left treeview. Expand this node and click the "Shares" option. The middle panel will be populated with all the active shares on your system. There are administrative shares you should leave alone -- these will have "$" appended to them. Everything else is fair game. Disabling a share is a simple as right-clicking on it and selecting the "Stop sharing" option.