you would go about it in different ways.
If the background was a pattern, you would assign it to the body and have it repeat x and y.
If the background is a fixed image (800x600), then you would probably want to center the image in the body. Having a picture that big is not recommended as it will take too long to load.
If you need a flexible background, I would create a background that can be easily repeated on the x-axis. That way it will extend as large as the screen resolution of the browser. Gradients work nice as repeating backgrounds.
Now, ideally, your page background/design is composed of several layers. You may have a repeating gradient in the background, but then some designs on top of that, and the actual page layout/design on top of that.
About your scrolling problem, my guess is that your image isn't in the background but simply included on the page.
Look here for more information: http://www.w3schools.com/css/css_background.asp
recently, I've been making a web page with a background image. The problem is, is that the image is too big and i need to scroll over to the right (meaning I'm assuming length is too big) where there's white space. Is there a way to get the web page background to fit any resolution. I tried google to look for the answers and most of them said something about setting a table width. Can someone also clarify what that is and how I can solve this problem?