Morphadaz,
The 3410A works seamlessly between the 2 inputs. After scanning in all available OTA and cable channels, you can scroll up thru the standard cable channels first then it automatically switches over to the OTA ATSC channels and then back to the QAM cable channels. I don't have a VHF antenna hooked up to my OTA input, just a Silver Sensor UHF, so I don't know what it does with OTA NTSC channels.
The guide is TVGOS which is being built into many of the newer sets. It works in mysterious ways as you may gather from the many posts in these forums about TVGOS. It is supposed to pull in guide info from either OTA or cable channels in the area. Many people have complained about it not working in their newer TVs but I don't recall any complaints from 3410A users.
For more info than you could ever want, look in the HDTV Recorders & Players forum for the 3410A thread that spans about 1.5 years. It is still active today.