Ok i got it now.
Do following :
Create one class derived from menu control.
Override render event
Protected Overrides Sub Render(ByVal writer As HtmlTextWriter)
Dim stringBuilder As StringBuilder = New StringBuilder()
Dim stringWriter As StringWriter = New StringWriter(stringBuilder)
Dim htmlWriter As HtmlTextWriter = New HtmlTextWriter(stringWriter)
MyBase.Render(htmlWriter)
Dim html As String = stringBuilder.ToString()
Dim strMouseHover = "onmouseover=""Menu_HoverStatic(this)"""
Dim strMouseClick = "onclick=""Menu_HoverStatic(this)"""
Dim str As Boolean = html.Contains(strMouseHover)
html = html.Replace(strMouseHover, strMouseClick)
writer.Write(html)
End Sub
Then overide Menu_HoverStatis(this) function as per below link:
http://forums.asp.net/t/1156758.aspx