Editing and security with .htaccess


I’m currently updating a site with a similiar approach the guestbook tutorial on this sides uses to add entries, which is writing to a .xml file through flash with a little help from a .php script.

Now, I don’t want anyone to update this side without a password. I was wondering if I could let any given .xml file in my public_html folder be writable as long as I protect the flash and .php file with .htaccess?

Thanks in advance :s: