Div height:0px does not work?

If you really want to be sure it’s gonna be have no height you could use something like this:

display: block;
line-height:0;
height: 0;
overflow: hidden;

If you’re still having problems on IE, you could also add

zoom: 1;

to it in a stylesheet targeted at IE with a conditional comment. That’ll trigger the hasLayout property in IE.

And display:none isn’t the same as setting it to zero height. Just look at the various clearfix solutions for a case where not removing it from the flow is crucial.