You can use the JavaScript split method to create an array from the selected drop down value and then assign the items in the array to the respective name field.
// form1.page1.name::exit - (JavaScript, client)
if (!(this.isNull)) {
var nameStr = this.rawValue;
var nameArray = nameStr.split(",");
form1.page1.firstName.rawValue = nameArray[1];
form1.page1.lastName.rawValue = nameArray[0];
}
Steve