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: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.

Do you mean like here - http://mudslide.vbulletin.net/ ?

Edit the header_background stylevar and under Background Image enter "url(http://url.to/image.png)" and repeat-x (or no repeat if it is the exact width) . I think that should do it.

That's handy for repeating a small image to fill the width.