Heres how i use this dll, obviously you will have to adapt the code to suit your needs, i have an RTB and a button whcih when clicked performs the spellcheck.

Heres how the code is:

vb Code:
  1. Private Sub SpellChecker2_DeletedWord(ByVal sender As Object, ByVal e As NetSpell.SpellChecker.SpellingEventArgs) Handles SpellChecker.DeletedWord
  2.         'save existing selecting
  3.         Dim start As Integer = RichTextBox8.SelectionStart
  4.         Dim length As Integer = RichTextBox8.SelectionLength
  5.  
  6.         'select word for this event
  7.         RichTextBox8.Select(e.TextIndex, e.Word.Length)
  8.  
  9.         'delete word
  10.         RichTextBox8.SelectedText = ""
  11.  
  12.         If ((start + length) > RichTextBox8.Text.Length) Then
  13.             length = 0
  14.         End If
  15.  
  16.         'restore selection
  17.         RichTextBox8.Select(start, length)
  18.  
  19.     End Sub
  20.  
  21.     ' Handles replacing a word from spell checking
  22.     Private Sub SpellChecker2_ReplacedWord(ByVal sender As Object, ByVal e As NetSpell.SpellChecker.ReplaceWordEventArgs) Handles SpellChecker.ReplacedWord
  23.         'save existing selecting
  24.         Dim start As Integer = RichTextBox8.SelectionStart
  25.         Dim length As Integer = RichTextBox8.SelectionLength
  26.  
  27.         'select word for this event
  28.         RichTextBox8.Select(e.TextIndex, e.Word.Length)
  29.  
  30.         'replace word
  31.         RichTextBox8.SelectedText = e.ReplacementWord
  32.  
  33.         If ((start + length) > RichTextBox8.Text.Length) Then
  34.             length = 0
  35.         End If
  36.  
  37.         'restore selection
  38.         RichTextBox8.Select(start, length)
  39.     End Sub

The above 2 just need placing in and the 'richtextbox8' replacing with your rtb.

And then on the button used to trigger the spell check this code:

vb Code:
  1. SpellChecker.Text = RichTextBox8.Text
  2.         SpellChecker.SpellCheck()