you really need a seperate power supply to power a peltier. Get a good big 350W psu to power two peltier, you have to make sure you give it not only the wattage, but the amperage to the peltier, that is really why you need a seperate psu for a peltier.
I dont believe you really need a seperate PSU for powering peltiers. Not if you buy a good PSU. I have an Enermax 431w PSU. Running everything I have listed below along with a slot 1 Alpha cooler and 3 case fans.
I dont have any problems at all.
As a matter of fact I ran all this only with a 50w tec instead of an 80w tec, on my old 250w PSU for about a year before I started having problems. After a while some things would not power up at bootup, including the peltier sometimes!
I dont think I would really put more then one tec on my enermax 431w but if you got one of there 600w psu's I know you could without any troubles. I actually would put another on but thats just me.
I'm with Dunno260 on this one go the seperate power supplies especially if you all ready have on that works ok, you might be able to use an old AT PSU if you have one laying around (just check with others before you use it).
I also am looking at water cooling a duel CPU board but I have no intentions of using 2 peltiers on the board, the heat coming of 2 would almost require you to leave the side off the case just to let out the hot air.
Instead I am looking at chilling the water before it goes into the water blocks I think this would be a more sensable approach (I think so, other may disagree)