not that they've very dear to me, but I ripped two 60mm fans from an old AT case I had (one from the psu, one front intake). they're designed for 5v. if I stick them on 12v, how long you think they'll last? and has anyone tried hooking up a ground wire to a -12v line on their mobo connector for a 24v line on a fan? that would be interesting...
i think you may have melty smokey mess on your hands if you try either of those, if that fan is supposed to by 5v then running it at 12v will certainly get you much much higher rpms, probably about 4 times as high, although it is likely that it will just burn out in a matter of minutes if not seconds bad idea mate
Actually the components in a good fan can easily withstand 12 volts, but it will get quite warm. I've run a 12 volt fan at 24 volts with no problems either. Don't be surprised if you get lots of magic smoke though