I'm not completely sure I understand what you're doing, but here's a go at it.
From what I can tell, you're creating an Alias and this has nothing to do with .htaccess.
Secondly, you put the Alias in the wrong place. It should go in the /apache/conf/extra/httpd-xampp.conf file and not the httpd.conf file.
Also, you do not need to create an Alias for xampp if your xampp folder is in your htdocs folder as you're showing. That makes no sense. I recommend changing everything you've done so far here back to default.
The xampp security isn't designed to keep on being used. It's designed to be used once as far as I can tell.
So that brings us to what you're trying to achieve. . .
THE .HTACCESS FILE.
This file is actually quite simple. With your text editor, such as Notepad, create a new text document, then put the directives you want in it. You can visit Apache's documentation on the .htaccess file for more info on that. http://httpd.apache.org/docs/2.0/howto/htaccess.html
I've also made a tutorial that explains the .htaccess file. MyOwnServer - .htaccess and .htpasswd
This is a really neat file considering everything you can do with it and I recommend reading more about it.
But yeah, you can leave the Alias off and just put a .htaccess file in your htdocs/xampp folder and you'll achieve what I believe you're trying to do.