Okay, I have found that a lot of time kernal panic syndrome is caused by memory.  Even if the test CD says its okay.  Try leaving just one in and rotating them to see if that helps.  I have had a couple of sleepless nights building macs from scratch and it always came down to the fact that the ram was bad or OSX just didnt like it.

Let's see if today it will let me post... : )

I have a slew of PC2700 RAM from OWC and Crucial. While I can easily test all the sticks because of that (they're all 512MB, too!), it'll just be really time consuming. I think I'm also going to clock the CPUs down by changing the multiplier from 6.5x to 6x (you can even do 5.5x which in my case would result in something nutty like 919MHz).

How about this: Since you started with a dual 867 Right? You can boot OS 9. It doesn't even take that long to install if you don't have it already. If its still unstable in 9, then its probably your bus overclock which is causing the problem. If it runs OK, its a RAM issue. You can even download and run DIMM First Aid if you can still find it. This will test all your RAM at once. If its the bus, you can add a heatsink to the Memory controller to see if that helps. If its RAM, try some 3200 if you have it.

I have PC3200 in there right now. There's some guy on Apple's Discussion Center telling lots of people to never put PC3200 in an MDD. Then again, this same guy said you can't do a 2x1GB config, which I responded to by providing a link to the Developer notes for the first MDDs showing specifically that a 2x1GB config is A-OK.

Thanks for the advice, War. I tried to flash the 9800 recently and didn't realize I never actually flashed it so I thought I did it wrong, got all bummed, realized my mistake, and just tried to do it again, only to realize that my computer now refuses to boot with my PCI Nexus128 card in place. It doesn't matter which AGP (if any) I have in there. Oh, well. There's always that VNC method or paying $25 to have some guy do it (and solder on the 128K EEPROM I bought).

This weekend I'll try and mess with the RAM. Which chip is the memory controller? Is it the big square on to the left of the RAM slots? If it's on the underside of the mobo, I doubt there're any kinds of heatsinks I could add to it.

Now to go find a place that sells 1000 ohm resistors. Another guy from Apple's Discussion Center said I definitely need 1k ohm resistors, but that apparently 0 ohms or a dead short work too. I think I'll stick with the 1k ohm resistors to play it safe.

The memory controller looks a bit like the CPU. Should be marked MPC something or other. Most of the older ones had a shiny purple metal surface visible. It should be between the CPU and RAM slots. I'll look in mine next time I get up...

Attaching a heatsink may not be straightforward, but its worth a try. I would say run it with the door open and hold the heatsink on, but I don't know how hot it would get and many stock MDDs actually overheat when run for any length of time with the case open. Maybe if you pointed a big desk fan at it.......

I don't see anything between the CPU and RAM slots. If it's there, it's under the CPU board. There's an Agere brand chip (pretty large) to the left of the CPU board, but I think that may be the Boot ROM chip since it says Apple on it.

OK... So, new info: The PC3200 Patriot memory I have is 2.7V when the MDDs have/had 2.5V slots. Could be a problem. Hard to say. The computer only crashes under heavier loads, so it's either unstable processors, overworked bus, or the RAM isn't friendly. Only way to tell? Crazy Photoshop routines, lots of 3D modelling, playing World of Warcraft (launching, logging in, and entering the world is no problem - it's moving around in the world that crashes it or the computer).

I found out that when I was out my wife used the computer for a lengthy period of time last night and it did not crash, but she wouldn't have been doing anything intensive.

Also, when looking for 1k Ohm SMD resistors on Mouser, I discovered it's not so simple... There's a +/- % tolerance, they have wattage ratings, temperature coefficients, packagings, and more. Guess that if I'm going to drop down to an even 1GHz (well, 1002MHz), it's going to take more research.

I can't see one on mine either. Got a sneaky suspicion its on the other side, using the metal of the case as a heat sink. Cooling that any further is going to be tricky.

3200 ram runs fine in the mirrored doors.  I too have two 1gb 3200 sticks and it has been fine.  I think that you should change the bus back to 133.  I would not be surprised if that is causing your problems. 

Thanks for that info, maestro. I still have yet to try setting the CPUs to a lower clock speed. I can go as low as 913 or so MHz before there's no point in having changed the bus speed. Naturally, if none of that works, I'll be back to a 133MHz bus. What'll be interesting is trying to overclock the CPUs with the 133MHz bus speed and seeing if similar problems pop up.