Yaw problems under power on snow/rain

[boro]

I find that when I drive on snow or in heavy rain the car yaws from side to side erratically while traveling in a straight line, but only when under power. If I clutch in, it rides straight.

The rear tires are a pretty worn because I have a rear alignment problem. The passenger rear would not return to 0 toe so it is set at 1.4* in, and the drivers rear it toed out 1/4* to match. So it does walk out, would that cause it to snap back and forth in the snow? I almost spun on the highway at 35 mph going to see my grandmother in the hospital..

When it does hang out it will hold to one side for about 3 seconds and then yaw over to the other side for about 1-3 seconds depending on speed and the amount of snow. It switches back and forth until I get to a dryer surface.

Some things I have been wanting to replace:
Motor mounts
Inner tie rods (rack?)
Rear tires of course
Struts

What else could cause this? As it is, it too dangerous to drive in the snow with other people around but it's my only car that will hold up in snow.

I would appreciate any help.

[boro]

thanks for your help..

[ericem]

You need to have 4 tires that are the same size and have even wear. Also check wheel pressure.

[boro]

Tires and tie rods are my next investments, but this seemed a bit too eatic for tires, though I am not ruling it out. It's unstable and unpredictble as if the wheels are gaining then losing power at random.

Could it be signs of a differential problem?