If you look at this: http://en.wikipedia.org/wiki/Molex_c...r_Connector.29
It sais the max A/pin is 11A. So 11A*12V = 132W. Also notice the 30C temp rise on the wikipedia rating.
I would say it is safe to use a PCIE 8 pin or 4 pin 12V connector. After all the latest video cards can use over 100W of power. You just have to be careful with the wiring. Also make sure your PSU can supply that amount on the 12V rail (most can do over 11A).
Also there is a difference between the W that the TEC consumes, and the W that the TEC can transfer from coldside->hotside. If the 100W is the amount of heat it can trasnfer, then it most likely means that the TEC uses more than 100W to move the 100W of heat.
A lot of people here like to run the TECs from a seperate power supply (including myself), it is safer and less chance of ruining your PC.
As to using nail polish, yes it can work. The stuff i bought was pretty crappy (Hard as Nails) it peels off easily from the board... Also the nail polish is only for waterproofing the motherboard in case water touches it. It does not prevent condensation, see the link Elloquin posted, it seems best.Edited by cmolson - 5/17/10 at 8:36am