Auto-X-ZTS is right. You definately don't want to put just two snow tires on the front of a FWD car. What you need to think about, is that although forward motion traction is important, it is more important to have overall stability for braking and turning in order to keep you pointing in the right direction. If you have to get on the brakes hard, the fronts will bite and the rears will not. If you're not going absolutley straight (and maybe even if you are), you'll probably end up pointing the wrong way. Also, if you're turning and the fronts bite and the rears don't, the same thing is going to happen. Perhaps even quicker.
If you can't afford four snow tires this year, I suggest going to the local junk/salvage yards and try to find four stock 14" or 15" wheels with some decent tread left on the tires. A skinny all season should be much better in the snow than the 712's in a 205/50-16 (I'm just assuming that's what you have). The skinnier the better.
On the other hand, I've had pretty good luck with running just a pair of snow tires on the back of RWD cars. It still doesn't help at all with braking, but it does give you the ability go get moving when you normally wouldn't be able to. And its relatively safe with the snows on the back since it actually reduces oversteer. But you still have to keep in mind that although you were able to get moving, the chances are that you are going to have a tough time coming to a stop.