A combo would work but methinks I might use a listbox. Have ALL the associated fields permanently in view rather than one. Also, when viewing existing records a combo won't distinguish which is which until you drop it down, and if it's bound but editable then that's asking for trouble.
This is a case where rigged database design is required because fundamentally rhe business approach is weak. If you can't remember your employee id you shouldn't be working there. That's my 2 cents