I would advise you to use a single method that will render the correct content by checking the selected value...After all that method runs on the server in the very same page where the drop-down is...
<table><tbody><tr>
<%=render()%>
</tr></tbody></table>
public string render()
{
swtich(dropdown.SelectedValue)
{
case: 1:
{
}
break;
case: 2:
{
}
break;
}
}
The Change method of drop-down will be used only for page refresh...