If this is just a look up form or an employee information edit form, then
create the form based on your table or query.  Add a combo box to the top of
the form and choose the third option of the first wizard screen.  Complete
the wizard selecting the Employee ID as the bound field.  When you type or
select the employee Id in the combo the rest of the information will be
displayed.
If this is a form in which you are entering data that will not go into the
employee information table such as sales information, you don't want to sore
all the employee info in the table, only the ID.  In this case you will need
to create unbound fields on the form for the employee info.  You can then add
a combo based on the employee info table/query with all the pertinent fields
included in the combo source.  In the Afterupdate property of the combo box
place this code:
Me.NameofUnbound1 =Me.ComboBoxName.Column(1)
Me.NameofUnbound2 = Me.ComboBoxName.Column(2)
etc.
Columns in a combo start at 0 so that the second column in the combo is
Column(1).