Hello Michele,

Try this UDF:
Function ranpw(l As Long, ByVal ca As Long, ByVal cn As Long) As String
'random alpha-numeric password with length l and a minimum of
'ca alpha characters and cn numerical characters
Dim s As String, sr As String
Dim r As Long, i As Long

Application.Volatile
s = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklm nopqrstuvwxyz"
If l < 1 Or ca < 0 Or cn < 0 Or l < ca + cn Then
ranpw = CVErr(xlErrNum)
Exit Function
End If

For i = 1 To l
If l - i + 1 = ca Then
r = 52 * Rnd() + 11
ElseIf l - i + 1 = cn Then
r = 10 * Rnd() + 1
Else
r = 62 * Rnd() + 1
End If
If r 10 Then
If ca 0 Then ca = ca - 1
Else
If cn 0 Then cn = cn - 1
End If
sr = sr & Mid(s, r, 1)
Next i

ranpw = sr

End Function

Press ALT + F11, insert a module, and copy this function into the
module.

If you need a password of length 5 with at least 2 alpha and 2
numerical characters:
=ranpw(5,2,2)

HTH,
Bernd