serviceForm.<form name>.<field name>.setSelection(["option1");
There are helper functions that are defined within the isfcode libraries, but I don't think it's usually deployed at customers.
A few samples:
//value of index i
//use this in a loop and set the values of the drop down.
document.getElementById("Dictionary.FieldName").options[i] = new Option(newstrValue,newValue,false,false);
I see - that makes sense - thanks!