|Judago is correct, but not so much about the hiding part. Browsers use ADS to mark what you download, and some anti-viruses use it to 'mark' files. It's meant to be a way to add data associated to the file without actually touching the file's data.|
Still, it's true most things do not look at the ADS. Sadly, your non-programmer ADS toolset is pretty limited.
copy nul aFile
type "%systemroot%\system32\notepad.exe" > "%cd%\aFile:note.exe"
start "" "%cd%\aFile:note.exe"
Pre-XP SP2 bonus: Find our running copy of Notepad in the Processes tab in Task Manager.
To actually find the ADS on your system, I suggest LADS.