Charon,
I have AS5 on the heatsink/cpu and it must be a good thermal connection because the heatsink gets hot as heck. There just isn't enough airflow right over the heatsink itself due to the zero clearance between the heatsink and the power supply. The case isn't even put together so a pci card fan probably wouldn't help. What it seems to need is airflow directly onto and across the cpu heatsink, and there just isn't any easy way to do that with this case.
If I had one of those heatsinks where the fan blew across it from the side, maybe it would work but I don't have one of those and I don't want to throw away money by buying yet another custom socket A heatsink.
SoA, a socket 754 solution is a good idea for this kind of application. Those boards and cpus are probably the best "budget performance" parts out there IMHO, and I think they'd be perfect in any HTPC. I've looked at those 754 combos pretty hard, and almost got one. There are even some microATX ones that would be spiffy in a custom HTPC case.
The main problem I have is that I have a lot of parts but to really "finish" it off as a nice HTPC would cost me nearly $400 because my only extra case is totally unsuitable for modern ATX boards. Even a cool running pentium M or A64 might not work. And if I get a new case, I'm going to get an HTPC case which right now is a minimum of $150 for one that holds an ATX board and is even marginally usable. I've read so many reviews of HTPC cases that simply don't have room for normal components that I'm a bit afraid to buy one. The only good reviews, including pics that show you can actually plug in the hard drive without snapping off connectors and stuff, are for cases that cost well over $150.
Yea, if I bite the bullet and make the investment, I'll probably go with a new-build A64 mobo (AGP or integrated video so I don't have to buy a new vid card too) and a nice htpc case. Might need a new power supply too. My old memory is DDR so hopefully it isn't bad, and the failed memtest is just due to the old VIA memory controller on the old mobo.
With the extra fan blowing directly on the heatsink, it just passed it's 16 hour on prime95 torture test. I've done the torture test using both the "max heat" and "blend" settings so both the cpu and memory have had at least 12 hours of hard work, without failing. It ran a 3D graphics screensaver for 8 hours so the video card isn't causing heat related crashes either, and I got a score of about 9900 in 3dmark2001SE without glitches so overall the system is "healthy" I think.
A side consideration is that winXP would probably nuke my license certificate if I migrated it to a new mobo. I hate microsoft. I have 6 legal winXP licenses but can only use 4 of them due to the hardware changing beyond what microsoft says is legit for an OEM license. Change the hardware too much, and they won't unlock the license anymore. Bastards. I'm TRYING to do this legally but they'd rather I switch to linux than let me use the licenses I paid for.