For the Row Source property of the combo box create a query, that has all the fields that you want to be displayed in text boxes. If you don't want them displayed in the combo box, set Column widths property appropriatelly.
Say you have two text boxes on the form that need to be updated: txtStreet and txtCity. In the query the Contact is the first field, Street is the second field and City is the third.
In the AfterUpdate event of the combo box write something like this:
txtStreet = Combobox.Column(1)
txtCity = Combobox.Column(2)
Columns start counting from 0 so the second column has index 1, the third 2...