Have a look into CSS Media Types -
W3Schools Media Types - use CSS specifically for a print layout of your site. This allows you to customise the printout of your site without changing the look of the site in the browser. In your case you will have to change your CSS until you get it to print out as it looks on the screen. Remember, if you have a fluid (dynamic) layout (which you should and if you don't I highly recommend you change now! It's very annoying not having sites fill my whole screen!), if you have a fluid layout, then on large screens more text will be shown than on 800x600 screens but your printout will (almost always) be on A4 paper - in other words for different users the printout and screen versions will not look exactly the same. This is not a problem, just make sure your CSS makes it easy to print on A4 paper, regardless of scren size. Your Print Media CSS
should use fixed widths to achieve this.
Hope this helps,
Ed :)