User authentification

Hi everybody I've a NT4 Wks + Apache + Php4.01pl2 (CGI)+ MySQL 3.22 shareware as an intranet server. I need to have users input a password to acces some parts of the site. Does anybody know how to do that, knowing I don't want to use mod_php if unstable : the OS is just as unstable I don't want to have to reboot it twice an hour (pretty long to boot), it's a production server... I thought of .htaccess files, but don't know how it works, didn't find on Apache's site :[ Would anybody know a URL where I can get help on .htaccess ?? Thanks for any response