Forms :: New Combo Box Entry To Add Record In Table

On a form to enter some new client info, I want users to be able to select their UserID from a combo box for future reference to other users (ie; Who made these notes?). For various reasons I want them to be able to add their UserID to the combo list for future selection if its not already on there.

There is a table set up for users, simply called tblUsers, with a single field, UserID. A query from this sorts the list alphabetically, and the combo uses this query to populate its list - qryUserID.

Users can currently select from a list or write their own UserID in the box, however when they write their own ID it doesn't get saved.

I don't need any message boxes or checking, just add it and move on kind of thing. It doesn't need to refresh the list immediately, as the user moves on swiftly once completing 2 more fields.