You might also try VideoLAN. It's free and open source, and plays a ton of different file types. The latest version plays mts/m2ts files out of my AVCHD Canon HF10 camcorder just fine.
Grab Haali Media Spliter.... it will allow you to open m2t, m2ts, mp4 etc with Windows Media player. You will need however a Directshow filter to play the video inside that container.... for that grab FFDshow Tryouts - this can playback avchd and mpag2 streams.
(IMO) Forget all these freebie players. You end up having about 5 or 6 of them on your machine because they won't play it all.
Power DVD Ultra. About $100 and it plays EVERYTHING. AC3, m2t, m2ts,ts Blu Ray, Dolby true HD, DTS, DD, Cineform avi (with cineform codec installed).... the list is endless.
I'm using Nero 7.5 with Vista 64 and it works perfectly. I've tried Nero 8 and 9 and was very disappointed in both packages and I've been a Nero fan since way back. Nero Showtime used to be a nice addition, since it played so many formats, but now there are so many free players out there, like VLC and Media Player Classic that Showtime is beyond useless.
For previewing HDV to customers I currently use GOM Media Player full screen at full res and I think the footage looks slightly better than the alternatives. A bit more contrast. VLC is OK though.
All you need is Media Player Classic. FREE. Doesn't need to be installed, just run .exe. Has built-in MPEG-2 decoder. If you also install FFdshow, you will play any video.
Media Player Classic - Home Cinema is Media Player Classic brought up-to-date, with support for hardware accelerated h.264 decoding and the EVR renderer (used in Vista).