Hi,
Assuming you mean can you use just a bit of PHP on a page containing HTML, the answer is yes, but the page must be called .php, or.php3, depending on how your webserver has configured the webserver.
All you do is...
<html>
(HTML code goes here...)
<?
//PHP code goes here
?>
(rest of HTML code goes here...)
</html>
As to writing HTML and PHP, I cannot recommend enough HTML-Kit, from http://www.chami.com. Not only is it free, but it colourises code and HTML for you, very good for free software. I've also heard good things of Dreamweaver MX, but that is a leeetle bit more expensive.
Many thanks,
ucbones