Web Page Size

Just FYI:

Now days, most all computer users have a monitor that can display a resolution of 800 x 600 pixels or higher and a majority of them have 1024x768 or higher resolutions.  There are very few people who still use a 640 x 480 resolution screen.
Many Web designers design for a screen width of around 750 pixels.  This page size will fit on an 800 x 600 screen and allows a little extra room for borders.  This width will also work for all higher resolutions as there will just be a little more space between the edge of the Web page and the edge of the screen.
There is no "right or wrong" answer to the question.  You'll have to decide which size you want to design for, but the 750 to 800 pixel width page will fit onto the most screens without users having to scroll left and right, although a wider 1024 pixel page allows for more information.