[OpenLayers-Users] changing div size and openlayers size command

[MilesTogoe]

having trouble with OpenLayers in terms of window sizing.  What is the 
correct way to specify the relationship between the div and the size 
command in OpenLayers, especially when it goes into a div that may 
change size according to any changes in the browser window size. 
I have tried without much success:
#map {
width: 100%;
height: auto;
}

function init() {
map = new OpenLayers.Map('map');
map.Size(100%,100%);
layer1 = new OpenLayers.Layer.Image('citymap','/static/maps/citymap.png',