VS 2010 Yet another problem with webbrowser..

I am creating a small program for a class that auto logs and clicks to a certain page, puts in a message, and send it, all from the webbrowser and with one click..

I have all of that but here is a problem..

I would like to add a "Signature" to the end of the message on the board for the class, kinda wow them and teach them a new thing.

But I would like it to be where I can type the message and click the "Add signature" button at the end, and it adds it on to the message.

Here's my line of code I am using:

Me.WebBrowser1.Document.GetElementById("message").SetAttribute("value", Form2.Sig_Txtbox.Text)

Any help?:)