Aligning a header image to top, left and right

There are a couple of topics on this here, but only for the top and right side, and they weren’t much help, and I did a search, to no avail…so, my question is how do I align a header image so that it aligns to the very top, left, and right of the browser without having the scrollbar appear. I’m using Dreamweaver MX, and I don’t know anything about CSS, so if anyone knows please give detailed instructions.

I made an example pic below. The top image is in Dreamweaver MX, and the bottom is the way it looks in the browser. That’s from an actual site, but I forgot the link. The header image is 1000 x 178. Any help would greatly be appreciated, thanks.