conditional display of widget

I have a widget that I want to show only on the front page – that’s already taken care of. but I also want to show it only when the user is not logged in. I know the programming logic but when I try to implement it, I get an error. so what I would like it a sample code that works, not just the functions. also the addthis widget, there’s no point in having it on the contact page. how do I exclude it from certain pages? thanks.
souleye