Summary:
Optimize Web pages for 1024×768, but use a liquid layout that stretches well for any resolution, from 800×600 to 1280×1024.

One of the most frequently asked questions in my [1] Web usability course is “What screen resolution should we design for?” The full answer is a bit tricky, but the basic advice is clear:

• Optimize for 1024×768, which is currently the most widely used screen size. Of course, the general guideline is to optimize for your target audience’s most common resolution, so the size will change in the future. It might even be a different size now, if, say, you’re designing an intranet for a company that gives all employees big monitors.
• Do not design solely for a specific monitor size because screen sizes vary among users. Window size variability is even greater, since users don’t always maximize their browsers (especially if they have large screens).
• Use a liquid layout that stretches to the current user’s window size (that is, avoid frozen layouts that are always the same size).

[2] More…