Your question certainly isn't very clear but I'll assume that you can
place page B into "insert mode" if you pass the appropriate parameter
to it in your querystring. Also, I'll assume that you want to open
page B in another window. You simply need to add a javascript (client
side) event handler to the button and you should be fine.
Protected WithEvents btOpenPageB As HtmlInputButton 'this is the
declaration for your button on page A
Private Sub Page_Load(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles MyBase.Load
btOpenPageB.Attributes.Add("onclick",
"javascript:window.open('pageB?mode=insert','newwindow');")
End Sub
I hope this helps.
Bill E.