Try ATi's AVIVO (hardware accelerated H.264 decoding).  I haven't tried it yet, but I think I read that it's just a DirectShow filter.  Basically video card does the decoding, offloaded from your CPU, and supported on all RadeonHD 2xxx series or later cards (integrated graphics should still do it).
Your heat issue sounds like my old AthlonX2 - fan goes at like 6000+RPM under load, and I had to keep the case open to allow extra airflow.  Can you lower the core clock on your CPU? (my AthlonX2 couldn't) - you could do a downclock that way.

My custom cooler does work well, though it's pretty much $55 for a big chunk of metal (and some thermal grease).  Can do a stable 2.4 » 3GHz overclock without any noticeable (or significant) temp changes under load.  Probably could easily go further, but can't be stuffed (2.4GHz runs well enough)
Generally system instability is caused by the voltages not being high enough, if the mobo isn't cutting the power from overheating.  Memory timings are also a source of instability.  Obviously, more voltage = more heat energy to dissipate, so you'll need to watch that (generally, you should aim to keep the CPU under 70C under load).

Otherwise, a pretty good value build, though I do like my Core 2 Q6600.
If you could have waited, would've got a Phenom II when the prices come down - apparently AMD improved heat issues a lot with the Phenom II (also due to the die shrink as well).  You could still upgrade, but really not worth it...


EDIT: Oh, make sure you enable all the speed stepping stuff in the BIOS too.  Not sure if your motherboard has it, but if it has, install and enable Energy Saver if you haven't already.

(This post was last modified: 11/01/2009 01:03 AM by ZiNgA BuRgA.)