How To Write / Code Javascript (mouseover Event) Using C# Methods

yes client side must be java script but my qustion is not that.i am asking that can i use c# language to implement "actions" fired on "click side events" such as mouse over the reason for this question is that i remember some syntax of registering functions for particular events of formview, which are call when the event occurs (yes there ispostback involved" is something like the above possible for client side events using c# or even vb.net

protected void Page_Load(object sender, EventArgs e)
{
Label3.Text = "this is label three";
Label3.Attributes.Add("OnMouseOver", "testmouseover()");
}
protected void testmouseover()
{
Label4.Text = "this is label 4 mouse is working!!";
}