POST en vb.net

[seinkraft]

Bueno por el momento logre esto:

Código vb:

Private Sub btnUpload_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnUpload.Click
        Dim request As HttpWebRequest
        Dim response As HttpWebResponse = Nothing
        Dim reader As StreamReader
        Dim address As Uri
        Dim data As StringBuilder
        Dim byteData() As Byte
        Dim postStream As Stream = Nothing
 
        Dim username As String
        Dim password As String
        Dim file_location As String
        Dim tags As String
        Dim source As String
        Dim md5 As String
 
        address = New Uri("http://localhost/api/add_image")
 
        ' Create the web request  
        request = DirectCast(WebRequest.Create(address), HttpWebRequest)
 
        ' Set type to POST  
        request.Method = "POST"
        request.ContentType = "multipart/form-data"
 
        ' Create the data we want to send
        username = "user"
        password = "userpass"
        file_location = txtFile.Text
        tags = "coco nu_se"
        source = "http://www.seinkraft.info"
        md5 = "2ef87d61eb6c5d318760db51828d8d00"
 
        data = New StringBuilder()
        data.Append("login=" + username)
        data.Append("&password=" + password)
        data.Append("&file=" + file_location)
        data.Append("&md5=" + md5)
        data.Append("&tags=" + tags)
        data.Append("&source=" + source)
 
        TextBox1.Text = data.ToString
 
        ' Create a byte array of the data we want to send  
        byteData = UTF8Encoding.UTF8.GetBytes(data.ToString())
 
        ' Set the content length in the request headers  
        request.ContentLength = byteData.Length
 
        ' Write data  
        Try
            postStream = request.GetRequestStream()
            postStream.Write(byteData, 0, byteData.Length)
        Finally
            If Not postStream Is Nothing Then postStream.Close()
        End Try
 
        Try
            ' Get response  
            response = DirectCast(request.GetResponse(), HttpWebResponse)
 
            ' Get the response stream into a reader  
            reader = New StreamReader(response.GetResponseStream())
 
            ' Console application output  
            TextBox2.Text = reader.ReadToEnd()
        Finally
            If Not response Is Nothing Then response.Close()
        End Try
    End Sub
 

Y los parametros de la api son:
Parameters
* login: login
* password: password
* file: file as a multipart form
* source: source url
* tags: list of tags as a string, delimited by whitespace
* md5: MD5 hash of upload in hexadecimal format

Lo que no se es como hacer la parte del file (ahora esta echa asi nomas). No se como enviarlo como multipart

Alguien me puede ayudar con ello?