I"ve got a 750W power supply that came in my Alienware 101-B. I just upgraded to an AMD 955 BE and plan on upgrading to a pair of Sapphire 5850 Toxic editions within the next couple of weeks. I'm also running 4 internal hard drives, 2 of which are Seagate, and 2 that are Western Digital. Any idea on if I would be pushing my limit with 2 of these cards?
I am pretty sure that your PSU has power enough.
The CORSAIR HX750 is an impressive power supply with a very high efficiency and with only high-end components inside (only Japanese capacitors and solid caps on the DC-DC converters in charge of the + 5 V and +3.3 V outputs).
You should be able to pull it up to 900 W at very good temperatures.