You need to get a VRM to run a split-rail CPU (MMX).
You can still get them here and there. I purchased an HP 0950-3188 (Delta 0552806A) which will run an MMX CPU. You can search HP Parts for a description of this VRM. Cost is $20US...though I got mine surplus (BRAND NEW) for $8US.
The problem with my board is that there is a short between VCore and VI/O...so for now, I can't use it.
You can certainly up the CPU Multipler and run your 166 at 200 MHz...been there, done that...no issues whatsoever.