Tabs come after certain periods. If text goes over, it jumps to the next. So only way would be to either set tabs into different places or then using a fixed length font (such as FixedSys or Courier New) and doing following:

VB Code:
  1. Dim a As String * 50
  2. Dim b As String * 10
  3. Dim c As String * 5
  4.  
  5. rtb.Font.Name = "FixedSys"
  6. rtb.Font.Size = 9
  7.  
  8. a = "AAAA"
  9. b = "BBB"
  10. c = "%%%"
  11. rtb.Text = a & b & c
  12.  
  13. a = "WWWW"
  14. b = "XXX"
  15. c = "F"
  16. rtb.Text = rtb.Text & vbCrLf & a & b & c
  17.  
  18. a = "QQQQQQQQQQQQQQQQQQQQQQQQQ"
  19. b = "TTTTTTTTTT"
  20. c = "10101"
  21. rtb.Text = rtb.Text & vbCrLf & a & b & c

Hope this is of any help.