Problems with code when using SP List (1 Viewer)

[DinkyDon]

You can use exactly the same technique.
Create another combo, and make its row source the Distinct list of equipment.

Now in your Listbox add the combo as criteria for the equipment in the same way as the Client.

Something like;
Forms!Homepage!cboEquipmentList or Forms!Homepage!cboEquipmentList Is Null

Edit: I can't think of any sensible way to have the same combo search for both.

Can this be done in the same combo box, or would it require a new combo box?

 

[Minty]

A new one - I can't see any point or reason to search for two completely separate things in a single drop down list.
You will either be looking for specific equipment or a customer or possibly both, so have two drop downs.

You wouldn't have drop-down of car makes intermingled with wheel or engines sizes ( well I hope you wouldn't).