Sure. When you get the "Print" dialog box, go into the Properties for the printer driver and check the box for landscape, or however your printer implements that. If you meant can your program force landscape printing on the user, then probably not. It's the user's privilege to print the document any way they like.
Paul, I think Dale was asking how to force it to happen.
There is no way currently to force the page to print in landscape. The only safe way is to have a pdf. IE has ActiveX that changes settings, but that is IE with certain security settings. Until the CSS spec for page layout is used in all of the browsers, you are stuck telling the user to do it.