When you have a 2.6 GHz P4 or above, ALL lit fans have trouble when the fan is hooked up directly to motherboard for power. The lights flash when they should really stay stable. this is because the processor takes up over 70 Watts (some even more) when the conventional P4 has always taken up 40 watts. This is due to pentiums new hyperthreading technology.
Thus, the new P4s take up all of the power from the motherboard. So, components like fans, or temperature gauges will not work correctly if at all when plugged into the mobo for power. SO, whichever fan you do go with, make sure that you plug it in with the standard power supply which most fans come with.