CMS Made Simple Forums

i want to make my page only 800 by 600 px, is it possible?? and when viewers see it in 1024 by 768 px in right side  i want there some banners and google add.

You can contain the body size to 800 x 600 but no matter what size the see it in the right side will still be in the body and the stuff will take up part of the overall width area and any thing you have in the content that would normally make the page grow down will make a scroll bar on the page, height is not the best thing to limit...