[T2DMan]

Have a look at the code on zen.co.uk - Add favorites for firefox/opera/explorer

Worked perfect first time. Slightly different to the above versions that didnt work for me:

function makeBMark(title,url) 
            { 
    if (window.sidebar) 
    { 
        window.sidebar.addPanel(title, url,"");

    } else if( window.opera && window.print ) 
    { 
    var mbm = document.createElement('a');
    mbm.setAttribute('rel','sidebar');
    mbm.setAttribute('href',url);
    mbm.setAttribute('title',title);
    mbm.click();
    } else if( document.all ) 
    { 
    window.external.AddFavorite( url, title); 
    } 
            }

I then use the following html

<a href="javascript:bookmark('title','http://www.domain.com')">Add to favorites</a>