To all AKIMBO users...

[tempest]

There should be a way to have it to systematically resize to one's resolution

Well, there isn't really a way to do that properly. Of course you can do width:100% but it will just look cheesy. No matter how large the image is, it will eventually scale up and look pixelated. It also grows higher, which means that e.g. on my 1680x1050 screen the banner takes up almost have of the page if I do that.
That's why you shouldn't use banners that are blocked off on both sides. Instead, use a moderately-sized left-aligned image with a gradient that fades off into transparency to the right. Or right-aligned, or centered, depending on how you want it to look, but if it needs to scale to 100% width to look good, you're doing something wrong.
Or just remove the banner and add a logo instead, which can be kept small :P