Redisplaying for print

I have a 3 col page with 3 main divs: #leftcontent, #maincontent,
#rightcontent.

leftcontent (100px) and rightcontent(160px) hold elements that are not
needed for print (some images and forms).

I have set the body and html width to auto and got rid of the padding
and margins on the maincontent, setting its width to auto too. I have
also set leftcontent and right content to display:none; width:0;

However, on print preview, the pages resolutely maintain a 100px left
margin (where leftcontent appears on the screen) and 160px right margin
(where rightcontent is).

Anyone got any suggestions as to what I'm missing?

/P.