Simplest way is with an if statement, switch would work also.
In the Form's docReady event [form1::docReady - (JavaScript, client)] put this:
if(textField1.rawValue == 3) //if the textfield is 3, show subForm1
{
subForm1.presence = "visible";
}
else if(textField1.rawValue == 2) //if the textfield is 2, show subForm2
{
subForm2.presence = "visible";
}
else //if the textfield is anything else, do nothing.
{}