I use vegas to edit AVCHD files and find proxy_stream.dll excellent.
(it's free google it or download it here
Document sans nom)
It's a batch convert tool which creates an editable version (you can select the format) of your .m2ts files which are added to your media library.
what's even better is that you can also use it to switch back to the original HD files. So I edit using the .avi's generated by proxy stream and then switch back to the HD files just prior to rendering. Means you can produce edited HD on a rubbish PC!