The
majority of users have a screen width of 1024 of greater, only 4% are using 800*600.
If I design a site with a fixed width I use 1008 or 1000 pixels (1008 is divisible by all single digit numbers except 5) to allow for 1024 less a bit for scroll bars however I prefer to use a fluid layout. Another thing you may wish to consider is how many of your potential user will try to view your site with an ipod or blackberry.
I try to keep the main part of an article above the 600px height but if it is a long article I would right a synopsis in the visible part of the page and allow the user to scroll down to get the details.
I have created a site that is completely resizable (see my signature) and with a bit of work could look good in any size.
Regards
Bob