if (document.images) {
    homebuttonup       = new Image();
    homebuttonup.src   = "images/home-off.png" ;
    homebuttondown     = new Image() ;
    homebuttondown.src = "images/home-on.png" ;

    companybuttonup       = new Image();
    companybuttonup.src   = "images/company-off.png" ;
    companybuttondown     = new Image() ;
    companybuttondown.src = "images/company-on.png" ;
    
    portfoliobuttonup       = new Image();
    portfoliobuttonup.src   = "images/portfolio-off.png" ;
    portfoliobuttondown     = new Image() ;
    portfoliobuttondown.src = "images/portfolio-on.png" ;
    
    pressbuttonup       = new Image();
    pressbuttonup.src   = "images/press-off.png" ;
    pressbuttondown     = new Image() ;
    pressbuttondown.src = "images/press-on.png" ;
    
    contactbuttonup       = new Image();
    contactbuttonup.src   = "images/contact-off.png" ;
    contactbuttondown     = new Image() ;
    contactbuttondown.src = "images/contact-on.png" ;
    
 }
function buttondown( buttonname )
{
    if (document.images) {
      document[ buttonname ].src = eval( buttonname + "down.src" );
    }
}
function buttonup ( buttonname )
{
    if (document.images) {
      document[ buttonname ].src = eval( buttonname + "up.src" );
    }
}



function changeImage(filename)
{
	document.mainimage.src = filename;
}