The one I used at a Post Office in the Ginza had a language change "button" and once switched to English was quite simple to use. The major adjustment is that the Post Office ATMs are more like Cash Desks than the upright Cash Machines we're used to in the rest of the world. Of course, it only spit out Y5000 bills when I requested Y10000, so I just went over to one of the "tellers" who exchanged the bills into Y1000 notes.

Since you can buy either a bus or train ticket with a credit card, you shouldn't panic if you don't get cash at NRT, as long as you don't need to get off the JR system (N'Ex tickets include a transfer onto any of the other local lines, albeit not subways...which is why the combo N'Ex/Suica deal is well worth getting). Once you get to your hotel and settled in, you can go hunting for a Post Office or CitiBank ATM.