How would I code this menu in PHP? And if every page in my site will use this menu, will every page need to be a .php page?
If your navigation menu is in its own frame at the top of the page then the pages in the lower main frame can be php, html, pdf ... any thing a browser can display.
As for coding, let's keep it simple with a couple of main menu items, each with a couple of subitems.
<body>
<table>
<tr>
<td>| <a href="$PHP_SELF?item=1">Item 1</a> |
<a href="$PHP_SELF?item=2">Item 2</a> |
</td>
</tr>
<tr>
<? if ((!isset($_GET["item"])||($_GET["item]"==1)) {?>
<td>| <a href="mypage1a.html" target="main">Subitem 1a</a> |
<a href="mypage1b.html" target="main">Subitem 1b</a> |</td>
<? } else {?>
<td> <td>| <a href="mypage2a.html" target="main">Subitem 2a</a> |
<a href="mypage2b.html" target="main">Subitem 2b</a> |</td>
</td>
<? } ?>
</tr>
</table>
</body>
When a main item is selected the menu calls itself, sending the selected item. When it reloads, it displays a different second row depending on which item was selected.
When a subitem is selected, it loads the appropriate page into the main fram area.
Of course this can be elaborated upon by using images as buttons instead of just text links.
hth