There are still a lot of people on 800 x 600 resolution with 15" monitor. I have read that the present industry standard is 1024 x 768. I have 2 Desktops and 1 Laptop. 1 Desktop is on 800 x 600 (15" monitor) and other is on 1024 x 768 (19" monitor). The Laptop is on 1280 x 1024. With a good design and the proper use of CSS you can satisfy the majority of people viewing the site.