Here is what I ended up doing.  It worked for me, but is probably not the best way and feels like a hack.

function SetGridDisabledState(bDisable) {
            if ((myGrid != null) && (myGrid != undefined)) {
                if (isIE() == true) {
                    myGrid.Element.disabled = bDisable;
                }
                else if (isFirefox() == true) {               
                    // have to set attribute in FF.
                    if (bDisable == true) {
                        $("#myGridId").attr("disabled", true);
                    }
                    else
                        $("#myGridId").removeAttr("disabled");
                }
            }
        }

The only way I figured out how to do it was to manually find the grids element by its ID using jQuery, and calling jQuery attr method to mark it disabled.  Its a hack.  isIE and isFirefox are just functions we have to determine the browser. 

Basically, figure out a way to grab the grids html element (jQuery selector or GetElementByID) and set the disabled attribute of the element.  I used Firebug to examine the DOM and figure out which element to select.  There probably is a much easier way to do it but since nobody offered any suggestions, I had no other choice but to hack it.

Hope that helps.