It was obviously taking issue to the visibility property, becuase display worked fine. I ended up changing it around a bit to be:
function display(DivID,onoff){
if (onoff == "off"){
document.getElementById(DivID).style.display = "none";
}
if (onoff == "on"){
document.getElementById(DivID).style.display = "inline";
}
}
which works nicely with onclick="display('menu','off')" to turn menu off
is there a cross-platform function that does the same thing? or a function that i can physically put in my code that all platforms will register? more out of interest than need atm, because I'm working on this for a very small group of ie-users...