i know what you mean...
having come from using XBMC on the original xbox that would play anything at all.....
to move to the 360 is a right pain.
on one hand i cant be without my HD goodness, but the messing around is a right pain.
my preferances are as follows
.TS - first choice....
WMV-HD.. also perfectly good.
DVD - Use DVDshirnk to rip the movie+sound to a single vob file.
rename to mpg. make sure you have the correct Mpeg2 codecs install on the extender pc and also the AC3 filters for dolby playback.
HD-DVD - no process at the moment to stream and/or convert just yet.
H264 - dont know... i suspect it is possible to convert to WMV
Avi (Xvid/divx) - i use Encode360 to convert to WMV. Luvly app and its freeware.
other tools that will come in handy to convert to WMV are
AutoMKV (freeware)
WinAVI (commercial)
WMVMuxer (freeware)
Gspot and/or AVICodec (both freeware) for identifying what the video file actualy is.
it will tell you the rez used and the codec and the sound stream ETC.
i think the biggest challange with things like H264 and HD-DVD is getting them into some format that one of the WMV apps above will be happy to accept. so you might need to investigate maybe demuxing the original file into seperate vidoe and audio and then somehow getting them into a format you can then rebuild the WMV with.
for instance you can use windows encoder to make perfectly good WMV's. but windows encoder is mega fussy about what files it will accept as input. Encode360 is more forgiving and will accept a wider range of imput types.
AutoMKV and WMVMuxer will accept a whole shed load of different imputs, but are considerable more complex to use than Encode360.
sometimes it does occure to me that rather than using my PC to convert all and sundry for my 360 to play it back, it would be far eaiser to just run a vga cable to my TV from my PC and play whatever format i wish.
but then my 360 woudnt get any use at all apart from the odd high scoring run at GW.