In photoshop, the majority of my designs I set the width to 800px. Once I begin to create the html/css for it, I usually round off uneven numbers (ie a menu with a width of 233 in photoshop will become 250) This usually brings the width to 850-900px
oh, I know. Although I found this today which estimates worldwide internet users at 1,733,993,741 So if 1% of users still operate at 800x900px than that's about 17,339,937 people That's round about the population of a large city like New York.
SVGA Standard is 800x600 BUT most monitors are moving to 1024x768 HOWEVER my laptop is 1280x800 Arg so many choices guess it depends on your audiance. GRaphic designers and gamesr would have bigger screens, old people probably smaller ones (older computers) Google analytics has a nice breakdown of your visitors screen sizes i get about 30% use 1024x768 and only about 6% are smaller then that (every one is larger) i even have a 2% 640x480 :-P Just remember 1024 does not mean 1024, There is the scroll bar, the boarders (if any) etc just like height is height - all toolbars, title bar, mane bar.. etc
1024px is the minimum resolution a website should be build for. Since you also have to watch out for browsers making this resolution a little smaller with their borders and scrollbars, a maximum width of 950 - 1003 px is suggested and the lowest width is 779px; but very few people are using this resolution. Workforce Management softworks-workforce.com