1. In PHP you don't do anything, you can't make a login form in PHP since PHP is a processing language that runs on the server.Everything that has tags (<form>,<input>,<div>,<select>) is only HTML. The extension of the file is irrelevant. a PHP extension tells the server that the file *may( have PHP code that needs to be run before the output is sent to the browser, but it may as well have only HTML, case in which nothing happens and the file is eventually sent directly to the browser.
2. The answers is that you need to make your login form normally in HTML but wrap it in a div. On that div, use some CSS styles to position it however you want. Sample code below:
<div class="form_wrapper">
<form i="login_form" name="login_form" action="..." method="POST">
<input type="text" name="username" value="">
<input type="password" name="pass" value="">
</form>
</div>
then in an external CSS file (or defined inline in the head tag), define the class form_wrapper like this (note the dot in front):
.form_wrapper {
width:111px;
align:left;
text-align:center;
}
the rest is up to you.