As everyone has said, 5x7/6x8 is what the Focus uses. Anything you buy aftermarket is going to be an upgrade over stock. For a reasonable $100 or so a pair you can get Polk db's, which are a good all around speaker. You can spend as little or as much as you want, so keep that in mind...
Zetec....is that like Vtec or something???
Zetec Crew #103/ATX Faction #27 (retired)