AVCHD conversions

Since many of you guys are whizzes in the techno dept I would like to ask if anyone knows a way to convert AVCHD video to mpeg4 without losing tremendous amounts of quality. I know this is a video question instead of a camera question but hey, they both have a lens on them right?

I bought a JVC HD video cam a few months ago and finally got around to using it. Footage in the camera looks great. Looks great when I connect the cam to the TV or view the SD card on the TV. However, I used the supplied software to convert this to mpeg4 so I could upload/share it and it looks terrible, worse than my standard def camcorder. I haven't tried uploading the end result but I am afraid of the results I'll get since sites usually do their own thing as well to transcode it for their servers. You can also create a blu-ray disc with this footage but will need a way of playing those, and I don't have a blu-ray player (yet).

I know all about how this is a "high-end" format and that up until recently there were few editors that could handle it. But it's been out for a few years and there ought to by now be a way to convert it without it getting full of lines, jaggies and such. I was about to install Corel video studio that I got as a gift because I think it recognizes the format and see what it does, but I wanted to ask here before starting to mess with a whole new piece of software. And no, the supplied software does not have ANY parameters you can adjust as far as adjusting the quality of converted footage.

Thanks in advance for any assistance