I would accomplish your objective like this:
//First page: THE FORM
<FORM NAME="TheForm" METHOD="POST" ACTION="<? echo $PHP_SELF ?>?seepass=1">
<INPUT TYPE="PASSWORD" NAME="ThePass">
<INPUT TYPE="SUBMIT" VALUE="Let's rock it baby...">
</FORM>
This is very ugly. Do the design of the form yourself.
//Second page: THE AUTHORIZATION
<?
//Imagine the password must be "fLIPIS" :-)
if($HTTP_POST_VARS["ThePass"] != "fLIPIS"){
echo "No, mate. No way i'm leaving you enter here";
}else{
echo "Hello, fLIPIS. How's it going";
}
Now, two things. You should protect more this by using a check on $HTTP_REFERER (ensuring the form comes from where it must)
and also check $REQUEST_METHOD, that must be equal to POST. This prevent people from entering the URL on the URL bar on the browser.
This is a simple auth system. It's a basis. Develop more complicated (server Auth, MySQL lookup and then check) yourself (if you want to)
Hope this helps
fLIPIS
?>