I finally got my 360 a week ago and have been trying to find a way to watch HD
(.TS Specifically) on the 360 without having to trans code. Here is what I found get your .TS files and use this
HDTVtoMPEG2 this will allow you to combine the .TS files into one or I recommend 3 files (4600Mb each, One big one tends to have the audio lagging by the end of a two hour movie and they fit nice on DVD-rs). Then take those files and run them through this
DVBPortal TSConverter this will convert them to .DVR-MS, which is a native Media Center file format. Now you can browse to that file in Media center and play the file. Hope this helps anyone that was looking to do the same thing I was.