What causes a high pitched squeal in the dash of my honda crv 1998 2 wheel drive automatic transmission. It happens periodically when I have the blower turned on

Does the exhaust sound right at the tail pipe?Can you hear an exhaust sound?If it is VERY quiet,it may be a clogged catalytic converter and that can cause the problem you have.
It should be looked at in person, by a mechanic for an estimate before you change any parts.
2 estimates by 2 different mechanics never hurt.

Power steering pump. Fluid is either low or the pump is wearing out.

Check your power steering fluid level. If too low the pump will whine like that. Put some in it if low. Don't buy power steering fluid, automatic transmission fluid is the same thing and is much cheaper.

Does the high-pitch whine exist when the engine is just running? Not moving (transmission is not in gear)? Running but with transmission in neutral (coasting down hill)?

As long it is not an all wheel drive you can. Just put it in neutral and drive away

Four wheel High is what you need to use in snow. It is similar to your regular driving experience but your speeds should not exceed 45-50 mph. Shift through your normal gears as necessary and drive with appropriate caution. Four wheel High should be used only as long as driving conditions warrant, using it otherwise can cause unnecessary wear on your transmission and drive-train as well as lower fuel economy.

Four wheel low is used for pulling out of a ditch if you are stuck, going through deep mud or rock crawling. Four wheel low will also cause your vehicle to lurch every time you press the gas pedal.

check the alternator drive belt,it may be loose and squealing.
the alternator itself could be also making a noise.
start the car with the hood open and listen to it.
look if the belt is cracked,loose or wet from oil or water etc.
things like thermostat housings leaking coolant can cause something like that.

If you have an automatic transmission, locate and check the transmission fluid dipstick to ensure you have enough fluid.

If manual transmission, usually you can only check it by unscrewing a bolt. (the fluid lasts a long time and shouldn't leak -look for fluid on the bottom of the transmission or under the car..)

I have not worked on these, so I am just guessing.

The noise could also be not in the transmission perhaps..

Hi there, you are right... the squeeling from what you explained is the throw out bearing or release bearing .

Your rear brake pads are most likely worn to the wear indicator which can make a high pitch squealing noise. It is very common that it will squeal when backing up, but not when applying the brakes. 50,000 miles is about the average life for rear brake pads on your car.