there's a bloke in the car club that uses a GoPro. video quality is decent but sound never comes out well. once car speed and wind pick up a bit it just gets wind noise!
they need a model with an external mic input!
and for free/easy video editing, try Windows Movie Maker. it's pretty basic, but great for just clipping, adding/changing music, titles etc...although it doesn't support a lot of formats, so depending how the video comes off the camera it may need converting to .avi, .wmv etc..

