Finding and storing AVCHD files?

So, I finally got things rolling with my new HD camcorder. I finally figured out iMovie, for the most part, and getting my video burned to disc for viewing. I know, DVD is old school. However, I'm trying to store the actual video files properly on a flash drive until I get an external hard drive. I couldn't figure out how to get the individual video clips onto my desk top so that I could drag then into a flash drive. I couldn't drag them out of imovie or toast. So I took the memory card out of the camera and popped it into the back of my Mac mini. I clicked on the icon that popped up on my desk top and went fishing through the folders until I found little thumb nails of each clip. I did notice they looked labeled different, MP4. I figured I had what I need and dragged them on to my desk top. For the heck of it, and I'm glad I did, I did a quick burn of a few clips I had dragged out of the memory card and when I played it back on my DVD player the quality was terrible compared to when I pulled the clips right off the camera and into Toast and burned them. How do I find the actual HD clips on my memory card? I assume those are the clips I should store for long term in case I ever want to do something else with them? Any help would be great. Thanks.