Here is "supra" snow survival tips.
First you need some snow tires. (Mount them on either an old set of sawblades, or get some RAV4 wheels, they fit the Supra just fine.)
When you buy tires, get them in 205 55 16 size. This narrow tire will cut down better and give you more traction on loose snow and ice.
I reccomend studs if you can run them in your state, or at the minimum a good ice rubber compound will help out.
Brake early, and go easy on the gas, and you should be fine.
Take a moment when you get your tires mounted up and find a nice empty parking lot. Drive around and see where the limits are in your car with those tires. (You will want a full set of 4 snow tires.)
I sold my 4 studded snow tires on RAV4 rims to another Supra owner here in Boise since my larger brakes make it impossible to fit 16" rims on the car anymore.
If I needed to drive the car in the snow, I'd be stuck buying a set of rims that would clear my brakes, and then buy some narrow studded snow tires so the car would get around.
last, buy two 75lb tubes of sand. (Long bags of sand work best, you can set them up so they don't move, and you can still carry other stuff in your car.) I put them in two semi-circles in the rear hatch area and it worked out great. A full tank of gas also helps to have more weight over the rear wheels.
Have fun, and remember to brake early. (Especially if you do not have ABS.)