Windows 7 and mkv confusion

I installed the Win 7 RC the other night.  After getting things set up last night I have to say that I like it pretty well.  The main reason for changing is that I got fed up with trying to get mkv’s to play in SageTV (or WMP) and Vista x64.  No matter what I did, graphstudio never showed any kind of video output going on…no codec, no renderer, nothing, only audio.  So I decided to try Win 7 and read up a little on how to get mkv’s to work.  One site I came across said to use Haali Media Splitter and ffdshow or DivX 7.  I don’t want to install ffdshow on my PC.  It’s a little confusing to me, and I believe it was part of the cause of my troubles with Vista.  So I first tried DivX 7.  On Sage’s site someone told me that DivX 7 was for MediaFoundation that Win 7 uses and would be of no use on Vista.  However, when I install DivX 7 (Vista or 7) it shows “DirectShow Filters” with a sub-group of h.264, AAC audio, and mkv.  Any way, after installing it on Win 7, the mkv files don’t show up in Media Center and if you just try to open the file, it doesn’t know what to open with.  So I decided to rename it to a .mp4.  Sure enough, now the files show up in Media Center and will play with MC or WMP.  Since I’ve heard talk lately about whether mkv’s are being hardware accelerated or not I checked cpu usage.  It ranged anywhere from 20’s% to 40’s%.  Never being satisfied, I decided to uninstall DivX 7 and install the Haali Media Splitter like I did with XP or Vista 32 bit.  Now, with the Haali splitter, the mkv’s show up in Media Center.  But the playback was jittery; in WMP playback is fine.  But when checking cpu usage with the Haali splitter, it was almost nothing; I think the highest it got was around 12%.  So am I to assume that it’s being hardware accelerated now, but not with DivX 7?  And why does the Haali splitter work?  I thought that ffdshow had to be installed?  Another weird thing was that I watched a ripped DVD, and then I tried 2 mkv’s in Media Center again and this time their was no jitter.  I’m really confused, especially by the DivX.  I read that DivX made them work in the Media Foundation and that thumbnails were available.  But I don’t see thumbnails, and if it does work, why do I need to change it to .mp4?  I read something else about having to join a DivX group to be able to download some “tech preview” to make mkv work in Win 7.  But it’s an older article, so I don’t know if it’s still true.  But on the other hand, maybe it works correctly with whatever this download is instead of the regular DivX 7 download.  I’m waaayyyy confused on what I really need to do.