One of the problems of native AVCHD editing has nothing to do with the OS. It has to do with processing power. Most computers today, even with 3ghz dual cores, cannot do it properly. So it has to be converted to something that the computers can work with.

As I understand it AVCHD isnt designed to be played back raw, but decompressed.

If you want to play them in WMP, just download a powerful MTS Codec software like Aunsoft Final Mate.

Windows Media Player plays the "raw" files if you have something like CoreAVC installed.

VLC - VideoLAN Mac, Win Free
 Has interlacing problems.
 VLC has pretty much every codec built in so it can play any file format,
 but I find that the MTS files do not look that great (they seem washed out).
 If you have the correct H.264 codecs installed on your system,
 then Windows Media Player will in fact play them.
 
Roxio Toast v11 Titanium Mac $80

WinX HD Video Converter does  De-interlacing - $36  for Windows | for Mac 

Microsoft Windows Media Player

mts player Win free