[Max Taxable]

Here's what I do on this, in vBulletin3.8.x. No reason I know of that it wouldn't also work on versions 4 and 5.

Image code:

<a name="top"></a>
<td valign="top" style="padding: 0pt;"><table width="100%" border="0" align="center" cellpadding="0" cellspacing="0">
<td align="center"><a href="./"><img class="imageObject" alt="Your Forum Name" src="http://yoursite.com/images/misc/yourbannerimage.jpg" width="100%" height="100%" border="0" align="center" /></TD></table>

Then in extra CSS attributes, define the img class for IE compliance: (This is a MUST.)

.imageObject {
max-width: 100%;
}


And that's it.

Live examples:

The Dallas Cowboys Forums - Dallas Cowboys fan forum

US Messageboards - Opinion, News and Information

You can see the header image adjusts to your browser width. As you make it skinny, or wide, it moves like a 3 piece header would. It also scales down to whatever size any mobile browser would be.

BEST RESULTS: Make your banner image large in size, 1920 wide by whatever you want the height to be on fullscreen, 170 is a nice size. This way we are only ever scaling the image DOWN, not up and this really helps the quality for bigger screens.