Hi there!
Try something like this.
You will need to set the Textbox1.MaxLength property either through
the Textbox1 properties menu in the VBE or programmatically (somthing)
like this:
Private Sub UserForm_Initialize()
TextBox1.MaxLength = 5
End Sub

Then you can use the following code to monitor the length of the text
that has been entered with the following code, and do what ever you
want if the condition is true.
Private Sub TextBox1_Change()
If Len(TextBox1.Value) = TextBox1.MaxLength Then
MsgBox "Max length reached: Cannot proceed any further."
TextBox2.SetFocus
End If

End Sub

Hope this helps.

Kind regards

Bernie Russell