Thanks stworthy you are a life saver!
below in my version that loops in values developed as a plugin
(function($) {
$.extend($.fn.combobox.methods, {
makeLetterSelectable: function(jq){
return jq.each(function() {
var cc = $(this); // the combobox object
cc.combobox('textbox').bind('keydown', function(e){
var s = String.fromCharCode(e.keyCode);
var opts = cc.combobox('options');
var data = cc.combobox('getData');
var state = $.data(cc[0],'combobox');
for(var i=0; i<data.length; i++){
var item = data[i];
if (item[opts.textField].toLowerCase().substring(0,1)==s.toLowerCase() ){
if(typeof state.index== 'undefined' || (typeof state.index!= 'undefined' && i>state.index)){
cc.combobox('select', item[opts.valueField]);
state.index = i;
break;
}
}
if(i==data.length-1 && typeof state.index!='undefined'){
state.index= undefined;
arguments.callee(e);
}
}
});
});
}
});
})(jQuery);