Sorry I didn't get back right away but yes you can use the 3 to 4 pin adapter and go off a power supply lead. However, the specs on the 80mm quiet NMB fans show .06A and .72W. The stock intel P4 Sanyo Denki fan pulls .16A (no wattage listed but it should be around 2W) and intel expects you to plug it to the board.
Each fan header on my Asus P4T-E board handles .35A and 4.2W and the new intel boards (taken from the Intel D845PEBT2) can support .8A for the cpu fan and .3A on each of the other two fan headers.
So there sould be no problem running two NMB's (one intake, one exhuast) and the P4 fan from the motherboard. I would think most other new boards should be close to the same.
note: just thought some actual #'s might be of some help.
