function showField()
{
var choice = document.chooser.type.options[document.chooser.type.selectedIndex].value;

if(choice == "alpha")
{
document.all['alpha'].style.display = "";
document.all['numeric'].style.display = "none";
}

else if(choice == "numeric")
{
document.all['alpha'].style.display = "none";
document.all['numeric'].style.display = "";
}

else
{
document.all['alpha'].style.display = "none";
document.all['numeric'].style.display = "none";
}
}