1. Select the folder you want to make invisible.
2. Press F2 or right click on the folder and choose rename.
3. Press and hold the alt key and enter 255 using the number pad (press the Num Lock key and enter 255 using the number pad in the Right Hand Side) and then release the alt key.
4. Press enter. Now the folder appears to be a nameless folder.
5. Now what is the next step ? Yes, that's it, making the icon invisible. For that right click on the folder and select the properties.
6. Select the customize tab and click on the change icon button.
7. Now a new window containing several icons appear. Select a invisible icon from the window and then press OK button of the two opened windows. Now the invisible folder is ready.
You can use this to have fun on you friends by hiding the folders in their computers.