I want to be able to detect a character in a string.

For instance...if the user types in "AD45BS", I want to check if the 3rd character in that string is a "4".

How can I do that with a VB form in Excel?

I figured it out.

Dim z
z = Mid(myString, 3, 1)

The search starts at the 3rd character and moves 1 to the right therefore selecting the 3rd character.

 You can also create a loop to check for valid characters,
 Here is part of a code that works after the DIM initialize:

  ' Check for length = 12, and proper hex characters
    Do
        charlength = Len(CStr(Range("C" & (i + 5))))
        If (charlength = 12) Then
              j = 1: i = 1: x = 1
             CharString = (CStr(Range("C" & (i + 5))))
            Do
                Select Case UCase(Mid$(CharString, j, 1))
                    Case Is = "0", "1", "2", "3", "4", "5", "6", "7", _
                              "8", "9", "A", "B", "C", "D", "E", "F"
                    Case Else
                        Range("C" & (i + 5)).Select
                        MsgBox "Illegal Character ( Not HEX character ) in string " _
                        & Range("C" & (i + 5)) & Chr(10) & Chr(13) & _
                        "Character=" & UCase(Mid$(CharString, j, 1)) & " j=" & j
                        Flag1Error = True: Skip = True
                End Select
                j = j + 1
            Loop Until (j > 12) Or (Flag1Error = True)
            If (Flag1Error = False) Then
                Range("F" & (i + 5)) = "OK"
            End If
        Else
            MsgBox "Not 12 characters long " & Range("C" & (i + 5))
            Flag1Error = True
        End If
        i = i + 1: j = 1
    Loop Until (i > 25) Or (Flag1Error = True) Or (Range("C" & (i + 5)) = "")
    If (Flag1Error = True) And (Skip = False) Then
        Msg = "Error in Data - Call ClearData_FG"
        Call SendMessage(Msg, Title)
    End If