Let's assume your two additional fields are FIELD1 and FIELD2 and your In/Out field is called FIELDINOUT
in the ON EXIT property of FIELDINOUT you could have (assuming the field is a value list of 'in' or 'out' in a combo box)
Code:
If FieldInOut = "In" Then
Field1 = null
Field2 = null
Field1.visible = false
Field2.visible = false
Elseif FieldInOut = "Out" Then
Field1 = null
Field2 = null
Field1.visible = True
Field2.visible = True
Else
'Do your else here
Endif
This is a bit heavy handed if you are doing this for a lot of controls on your form so you may want to consider more elegant solutions if this is a more substantial form.