I'm finally able to get full speed playback of 720P 24FPS HD streams using the Elecard software MPEG player.
Until now I was only able to play 480P streams, the 720P streams caused major sound breakups and skipped frames.
My machine is a 1.2GHZ Athlon with VIA chipset. I was using the via4in1 drivers version 4.32 (latest). I decided to try the beta 3.12 IDE driver from viahardware.com .
All I can say is WOW! Even though the actual throughput according to my benchmarks didn't improve that much, the difference on my system is night and day. If you have a VIA chipset based system I highly recommend this driver.
I still get some skipped frames on 720P 30FPS materials as well as on 1080I ones, but even those are much more watchable now.
Getting closer to full speed software HD display every day...