.htaccess help

Hi,

I'm new to .htaccess. I'd like to do the following:
I'd like to disallow all requests for all files and subdirectories in a
certain directory, except for the index file (index.pl) for that one
directory (not for the subdirectories). I'd also prefer if the index.pl
file could still be accessed as the directory index.
Also, that file is only accessible if HTTP request header X-Client has a
value of MW.
I don't understand how to accomplish this.

Thanks,
Frederik Vanderstraeten