InstallDir - MyDocuments

Hello,
I want to make a default setup on Folder "My documents", and people cannot change this.
What i do on "InstallDir"??

i put this but don't working : InstallDir "$USERDOCS\Myprogram.exe"

Anyone can help me please?

If you read the section in the helpfile about "Constants" you should be able to find the variable you want...