Thanks Billy for the answer,
the first part is very clear, the second one I'm not sure that I understand: do you mean looping through the elements and modifying their tags by adding an onmouseover="myfunction()"...?
I'm not sure this will work, bceause the elements in my page are added dinamically by server scripts (that I cannot change), I think with Ajax or ASP.NET. Is there not a way to find out if I'm over them without needing to alter their tags, meaninng: whitout having to use the onmouseover event handler?
thanks