Hey I found an answer at the clublexus.com forum. The description I found there is "P2241 Front Air/Fuel Ratio (A/F) Sensor (Bank 2, Sensor 1) IP Line Low Voltage." So there ya have it; sensor # and location. Lucky for me it's the easy one. Unfortunately, it's also the more expensive one. Oh well.
Also found some tech tips on changing these sensors - it takes either a 22mm or a 7/8" sensor wrench. The front one can be access with the same size box-end/spanner/ring wrench, which ever you choose to call it.
Anyway, rather than re-write all this I'll simply recommend going to clublexus.com. Their forum is key word and phrase searchable. Also, toyotanation had some good info and they led me to clublexus. So, yeah, kudos to them.
Later