Stretching a banner

Is there anyway to strect a banner so it fits all the way across the top of my forum? If so, how? I cant create one that is wide enough to fill across the whole screen which is what I would like and just wondered if there is anything I can do about it?

You would actually need to use a graphics design program to be able to manipulate your banner. But for myself personally, I cannot figure out how to have the banner resize itself automatically depending on the screen size. So just take into consideration that if other members of your forum have a smaller screen size the banner may appear off center.

I recommend Gimp 2.0 for this project.