Ok, I dropped my A7V333R into my home system in place of my K7S5A. You can say what you like about Win98's stability, but it certainly is flexible... it blue-screened on the first startup, but it made it through the second one and I was able to plunge into a quick-and-dirty test of the thermal question (after installing 4-in-1 drivers, etc).
Asus Probe started off by claiming that my +12V voltage is 13.8V, which didn't give me a lot of confidence in it. It's not getting that reading from the BIOS, at any rate. Asus Probe showed my Win98 system idling at 58C, and I had specified 1-second update frequency. I switched on AP's software cooling by checking the checkbox, but the temperature sat at 58C.
Next I started SETI just to see what would happen. Over the course of two minutes or so, the CPU temperature rose from 58C to 60C. I stopped SETI and it fell to 57C over about two minutes' time.
Next I fired up trueSpace 4.3 and pulled up a scene with an hourglass. I made five extra copies of the hourglass and spread them around. The CPU has to work very hard to compute the reflections and refractions of glass, so I knew that would keep it busy for a while. I started the render session and watched the temperature. Over the course of about four minutes, it rose and peaked at 61C. I watched for about five minutes and then cut off the rendering and timed the fall in temperature. It hit:
60C after 35 seconds
59C after 1:17
58C after 2:03
57C after 2:43
From the lag in the temperature response, and the very small spread of temperatures, my initial guess is that the system is not getting its reading from the core diode, but rather from a socket thermistor.
I just thought of a method of testing that theory, which is to get the motherboard out of the case, locate the underside of the socket, and hold something cold against it while watching the temperature readings. If they drop quickly in response to a cold object on the underside of the motherboard, that would be evidence in support of socket-thermistor readings. Stay tuned (and wish me luck)!
EDIT: and before I try this stunt, let me say that MyLogo ROCKS!

It is very easy to do.
1) get the image you want, and use a quality image editor to reduce its size to 640x480 pixels, then convert it to 16 colors. I recommend making it into a GIF with 4-bit color (which is 16 colors), using PaintShop Pro or something similar (you can download a trial version if you need to). After getting it into 16-color mode to your satisfaction, choose
Save As... and save it as a BMP file.
2) download the BIOS from
Asus, even if you don't need to update to a new version. Save it on your hard drive.
3) After installing the Asus Update utility from the CD that comes with the motherboard, go to Start > Programs and launch the Asus MyLogo utility. Tell it where to find the BIOS you downloaded to your hard drive, and then the image you've made. It will replace the stock A7V333 logo with your own logo.
4) Now you have a customized BIOS file, and you just need to run Asus Update from Start > Programs and install your custom BIOS.
I have my Cheetah avatar at startup now, very appropriate since I will have a Seagate Cheetah X15-36LP in there

(assuming I don't destroy my motherboard in the cause of science first

)