Yes. But I would go with with an 850 watt PSU.
Figure about 10 amp for the CPU and 30 amps for two video cards. That's 480 watts. Figure 100 watts for the motherboard and 50 watts for 2 HD's and an optical. That is about 620 watts.
I fure that is a high side estimate of power consumption. One of my systems has an OC'd Q9550, 4 GB RAM, a GTX260 - a card with similar power requirements to a GTX560Ti, a Gigabyte EP45-UD3P motherboard, 3 hard drives and an optical, and a Soundblaster card all powered by a Corsair 750TX.
Running 3 instances of Prime95 to load the CPU and 3DMark06 to load the GPU, it pulls 375 watts from the wall as measured by my Kill-a-Watt meter. Figuring 80% PSU efficiency, the system pulls 300 watts from the PSU.
Using this data, I'd estimate that system power consumption with a pair of GTX560Ti's would be around 500 watts.