HDC-HS300- Importing files to PC

I've bugged my eyes out researching and trying to learn this (I admit I am green at this), any help is appreciated.

I bought the Panasonic HDC-HS300. When I connect the usb to import my movies (using HD Writer AE 1.0, supplied with camcorder). When I browse into the HDWriter program afterwards the files are .mt2s. I understand this file type is heavy for a computer to run, for example when I try to play it in windows media player it lags, drags, lines...

There must be a simple solution to how I can import movie files from my camcorder onto my pc, and be able to then load them into WMM or SonyVegas to edit and create a movie.

I don't want to lose any quality and am trying to learn it all.. thanks.