all css properties can be modified via js, but notation is different (background-repeat is backgroundRepeat etc.)
// foo is <td id="foo">
var o = document.getElementById('foo');
var s = o.style;
s.background = "url('a.gif')";
s.backgroundRepeat = "repeat";
in your code, I think that "o" is "bDiv.firstChild" ...
You can probe any object to see it's properties:
if (typeof s == 'object') {
for(key in s) document.writeln(key+':'+s[key]);
}