Silly question I know, but those are the hardest answers to look up. Simply put could I put a 1.2 Mhz CPU in my MSI K72turbo (I think) MB. It is about 1,5 years old now, and doesn't seem to support a 266 bus. Would a 266 chip run at 200, or not at all?

I have the same mobo but u have to check the revision i think. I don't know if all revision have the tk133a chipset but if u have this chipset it means that it support the 266fsb. I know that i have the revision 3.0 with a 1,3Ghz Thunderbird and it work. In the user's manual it said that it can support cpu up to Athlon XP 2000. So check for the chipset, if u have the kt133 it will not work, i've already try with a different mobo with that chipset.

I don’t know the answer but I’m very curious to know it. I’ve got an AMD K6 II 400Mhz with an FSB of 100MHz that I’ve run at 75MHz before but I don’t know if this is true with Athlons or Athlon XPs.

Even if it only supports 200 Mhz it should work. Its just that the chip will be clocked lower, because the FSB is 133 Mhz lower. So if you have a 1200 MHZ FSB 133 CPU, it will run as a 900MHZ FSB 100 CPU. If that is the case, you could do the pencil trick to unlock the multiplier and put it back up to par.