Don't worry! I had absolutely no problems with the board, after these mods (stability-wise), except for the fact that it didn't want to do any higher FSB. Seems as if I just had the bad luck with a lousy northbridge chip. Everything above 230 MHz was unstable, even with more than 2V Vdd (but as I thought about it, that could've been due to a shottky diode, that according to A666 limited the VDimm to 2,9V, regardless of the selection through the mod) .
Anyway, sold the board and got me a DFI Lanparty Nforce2 Ultra B in the meantime, that'll be modded the next few weeks. And a nice A64 system is also here now, again with a DFI Lanparty board.
Will do some heavy modding next month.
Wish me luck. If everything turns out right, then perhaps there'll be some new guide's up here again (Topower 520W modding???, DFI Lanparty Ultra B vmods and cooling mods and Lanparty Nforce3 250GB UT about the same; ah and Tagan 480W PSU is also here and ready to be vmodded). We'll see.