That's a good question. It depends on how the program was written. If it was a more modern game, it was most likely designed to take advantage of 2 cores. In this case a 1.7GHz dual-core would be better. However, if you're playing an older game, then the 3.6Ghz single-core would outperform the dual-core.
so lets say pcsx2 (if you know what that is) since that utilizes two cores the 1.7 would be the better choice for running that program?
Also if i WERE to play an older game, would it only run only on the 1.7 GHz processor as if there wasn't a second?
This only works if the processors are identical other than the number of cores, which they won't be. Clock speed is one of the least important factors in actual processing speed. The architecture and technology on the chip is what makes the difference, clock speed can only be used to compare processors within the same series.