The OP doesn't want the users to have to click to close the Messagebox...and the answer to that is 'no.' As you suggested, you'll have to create a Form and with a Timer event close it after X number of seconds.
The code to close it is simple. Assuming that the Form is named RecordAddedForm...
Code:
Private Sub Form_Load()
TimerInterval = 3000
End Sub
Private Sub Form_Timer()
DoCmd.Close acForm, "RecordAddedForm"
End Sub
An Interval of 3000 is for 3 seconds, but it sometimes takes a second or two before the Timer kicks in, so adjust that as you wish!
You'll need to open RecordAddedForm as you unload your primary Form.
Linq ;0)>
The problem with making anything foolproof...is that fools are so darn ingenious!
All posts/responses based on Access 2003/2007