Q1:How can I get the document width and height?

A: Internet Explorer - use (document.body.clientWidth - document.body.clientHeight)

Mozilla - use (document.body.clientWidth - document.body.clientHeight) or (window.innerWidth - window.innerHeight)

Netscape 4x - use (window.innerWidth - window.innerHeight)
Netscape 6 - use (window.innerWidth - window.innerHeight)

Opera - use (window.innerWidth - window.innerHeight)

The best thing to do is object detect

//opera Netscape 6 Netscape 4x Mozilla 
if (window.innerWidth || window.innerHeight){ 
docwidth = window.innerWidth; 
docheight = window.innerHeight; 
} 
//IE Mozilla 
if (document.body.clientWidth || document.body.clientHeight){ 
docwidth = document.body.clientWidth; 
docheight = document.body.clientHeight; 
}