When I was getting that same set of codes, intermittently, it turned out to be, not the sensor itself, but a dirty connector.  Cleaning the connector made the problem go away.  You might wanna try the same before you invest in new sensors.  You wouldn't be able to tell this with your code reader, but using Alex Peper's CarCode product, I was able to diagnose this problem by watching a live graph of the O2 sensor readings.  They would mostly work correctly, but occasionally drop to zero and stay there for a while.  Jiggling the connector made them return to normal.

  In any event, I believe the codes you're getting indicate a problem only with one sensor, which would be the Bank 1 (on the Duratec, is that the bank toward the front of the car, or toward the firewall?) sensor before the precat.

{I do hate spam, but that isn't really part of my email address.  Remove the string ?HatesSpam? from the email address ?BobHatesSpam@blaylock.to? to email me.  No advertisements.  Spammers will be dealt with very harshly!}
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Moonlight Blue 1996 Mercury Mystique GS , Zetec engine, ATX.  No mods. (Well, OK, one mod.  Before I got rid of my previous car, a 1994 Tempo, I swapped radios.  I liked the Tempo's radio better.  That counts as a mod, doesn't it?  I also kept one of my Tempo's wheels to use as a spare.  I hate those stupid ?compact? spares that come with modern cars.  Does this count as a mod?  If so, I guess I have two mods.  Replaced burned/melted blower switch and connector on 19 February 2002 with a 1P3T toggle switch from Marvac and a Molex connector from Rat Shack; I guess this now makes three mods.)