Big thanks for putting this together! I just went through the steps, and I'm now watching 720p mkv rips on my little acer aspire one netbook with Ubuntu 9.10 Karmic. If anyone else is in the same boat as me I had to do a couple of additional tweaks in smplayer to boost performance, specifically:
-video output driver: gl (fast)
-enable direct rendering
-audio out: alsa
-threads for decoding h.264: 2
-Loop Filter: Skip only on HD videos
Now I don't have to buy a broadcom hd card or coreavc. THANKS!