if this is your website then just change this <input type="submit" value="Join!"></td></tr> to this
<input type="submit" value="Join!" id="Join!" ></td></tr> and this should work fine WebBrowser1.Document.GetElementById("Join!").InvokeMember("click")

if this is not your website then use this

Dim HTML As HtmlDocument
Dim HTMLI As HtmlElement
HTML = WebBrowser1.Document
For Each HTMLI In HTML.GetElementsByTagName("input")
If ElseIf HTMLI.value = "Join!" Then
HTMLI.InvokeMember("Click")

End If
Next