By holding down alt, then typing numbers on the number pad (right of the keyboard) you can create special characters.
If you hold down alt, then press 1, then let go, you got the ascii character 1. You try some randomn numbers. This goes all the way up to 255.
Open a dos prompt, and type md (alt+1+9+4)someword.
md is the dos command to make a directoy,
now try and open the directory in Windows, you can't.
To open it, type ren (alt+1+9+4)someword someword (ren is the dos command to rename).