You can do this using 'scalable' pictures and percentages for table sizes instead of pixel values. So the base of the website is a table which is 100% width. Split it into the number of columns and rows you need (a column for the left nav and main content; and a row for the header and the nav/content section. Basically its 4x4. That is the most basic, but what you want depends on the design). The key here is to use graphics that are either a solid colour, tileable or a gradient. Gradients are good because they can be stretched in the direction opposite to the colour change. Try this quicky in photoshop. Make a gradient from top to bottom and scale it from left to right. It will not loose quality.
So now the key is to use tricks like make the page with three columns. Pur a the side columns will have fixed pixel values and they can have graphics that don't need to get larger. Then the middle section will have a percentage value of 100% so it fills the screen. Any graphics in here will have to be scalable like I said above.
This info is pretty general, I hope it makes sense.
