The "VSC" light came on on my 2003 Toyota Highlander. What does ths mean and what should I do? Is this a expensive procedure to fix?

Temporarily on and off or on all the time? On a wet or snowy road.

Here's a possibility:

. Ensure the gas cap is tight. Tighten the cap 3 clicks, after seating the cap.

. Reset the ECM, by using a code reader or scan tool. Disconnecting the negative battery cable for 15 seconds may work--be sure to record any radio codes first.

. Stop pumping gas into the fuel tank, after the pump clicks off. Fuel may be expanding into the charcoal canister and throwing the VSC/TRAC codes. Topping the tank off, after the nozzle clicks, can result in serious damage to the charcoal evaporative emission system.

The Vehicle Skid Control (VSC) Light and the Traction Control (TRAC) Light are turned on anytime the Check Engine Light (CEL) comes on, because both systems are disabled at that time. There is probably nothing wrong with those systems--the root cause is likely the CEL coming on, due to overfueling.

If you damaged the charcoal evaporative emission system, repairs can easily run $500. Check for any codes.

VSC (vehicle skid control) is part of the ABS dynamic braking system. Sometimes they go off calibration like when you change out a battery or have the front end aligned.
Most likely the steering angle sensor is off center. It must know when your steering wheel is straight ahead.
Be sure your tires are all the same wear, brand, inflation. This is important too.
This will require a recalibration and Toyota can take care of this with the scan tool for a minimal charge.