For Web sites, I recommend a design width of somewhere between 800 and 900 pixels.
I generally recommend against using a liquid layout format, except in cases where the web site is meant to be highly searchable and is connected to a database that has a large number of important fields to be referenced.
A width between 800 and 900 pixels will fill much of the screen at a screen resolution of 1024 x 768 pixels, allowing you enough room horizontally to build navigation menus that can contain ten or so links. This will also allow you to build a vertically oriented navigation structure on the left or the right side of the page, in addition to the horizontal navigation structure, giving you room to grow and expand content in the future.
Having this fixed width of 800 to 900 pixels also allows you to preserve the integrity of the design elements across several screen resolutions, and ensures that your design elements will remain in the same proportions regardless of what screen resolution the user has selected.
