m2t is what's known as an MPEG transport stream. It's for all practical purposes an MPEG2 file as you can see by changing the name as you did. Really there isn't a need for any software which can handle m2t files.
I'm not sure what you're saying about the importing. Can you explain more? What is labeled tape device?
Basically, for a quick run down of how the system works:
1) Image is captured by the camera's CCD
2) This image is processed by on board components and changed from analogue -> digital (electric current -> 1s and 0s)
3) This newly processed footage is recorded to tape digitally (ie binary)
Since the signal recorded to tape is 1s and 0s there is no loss of quality when making a copy of the footage like you would get with an analogue tape. You can bring footage from the tape into your computer without loss as long as the tape itself holds up. In your case this is a full HDV signal. This is NOT DV. It is not recorded to the DV spec ; it's recorded as an m2t file. For this reason anything you bring in from firewire will be MPEG2 HD. If you want to downconvert this footage to SD you will need to do this in your NLE (that goes for the Sony as well). The camera _can_ downconvert this footage if you connect it straight to your TV though (because it has to be processed to an analogue signal it can be altered fairly easily on playback). This is only to keep the camera compatible with current SD TVs and is not recorded to any medium at this res. Now, the Sony CAN shoot standard def DV as well as HD but that is quite different from converting a HD signal to a SD form. The SD on the Sony is rather lame actually. I personally cannot see why anyone would use it but that's just me.