Keeping fields out of URL

How can I keep fields in a form out of the URL? I am writing a basic PHP/login script to password protect a directory of the web site (if anyone knows of something pre-made, please do let me know). But, the first stumbling block is that when sometypes in their username/password, even when the I use th INPUT Type Password so only asterics appear when it is typed, the password still appears in the submit query URL. How do I stop that? Ryan Shrout