VS 2008 RichTextBox NewLine/CurrentLine/SelectedLine

Hi. I want to make a private program that navigate sites wrote in richtextbox, like that:

Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer1.Tick

Progressbar1.Increment(1)
If ProgressBar1.Value = ProgressBar1.Maximum then
ProgressBar1.Value = 0
WebBrowser1.Navigate(???)
End if

And yeah, i want for example:
RichTextBox1.currentline + 1
RichTextBox1.NextLine
Etc, but no one works. Please help me, i'm not new in VB but i don't know that.
Thank's,

Bogdan.