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  WebBrowser1.Navigate('url');
  WebBrowser1.OleObject.document.forms.item(0).elements.item('feldname').value:=edit1.Text;                    

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procedure TForm1.Button1Click(Sender: TObject);
begin
  WebBrowser1.Navigate('http://myspace.com/');
end;

procedure TForm1.Button2Click(Sender: TObject);
begin
  WebBrowser1.OleObject.document.forms.item(0).elements.item('email').value:=email_edit.Text;
end;                    

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   <form action="http://login.myspace.com/index.cfm?fuseaction=login.process&MyToken=7cce6ab9-28bc-4b1d-ad10-a5aa22c3f508" method="post" name="theForm" id="theForm">
[...]
        <div class="row">
            <label for="email">
                E-Mail
                :</label>
            <input type="text" name="email" id="email" value="" />
        </div>
[...]
    </form>
</div>                    

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WebBrowser1.OleObject.document.forms.item(0).elements.item('email').value:=email_edit.Text;