You can use key trapping by their corresponding ASCII equivalents and Case statements.
Example:
Private Sub Text1_KeyPress(KeyAscii As Integer)
Select Case KeyAscii
Case 65 To 90, 8, 32, 39 ' A-Z and backspace and space Let these key codes pass through
Case 97 To 122, 8 'a-z and backspace Let these key codes pass through
Case Else
KeyAscii = 0 ' Traps other characters
End Select
Try to find the complete ASCII table. Would be useful. Cheers :)