One simple way of doing it is to:
1. Create a messages table containing fields UserID (text), MessageText (text), DateTimeSent (date/time), MessageRead (yes/no).
2. Create a form that is open hidden when the database is launched. Give this a timer event to check the table for new messages delivered to the current user. If a new message is found open a frmReadMessage to display the relevant text.
If you open frmReadMessage as acSystemModal (IIRC) then the form will be displayed on top of anything they are viewing - even if they are not focused on the Access window at the time (it should really be acSystemPopup, rather than acSystemModal).
The timer event shouldn't run too frequently to avoid unnecessary overheads - once every few minutes is plenty.
I have an example that I can share on Monday if you like...
Ed Metcalfe.
Please do not feed the trolls.....