The disable switch for the passenger side airbag was added mid-year of the 2000 model year.
Note: the NHTSA says you must obtain a waiver from them in order to get an airbag disable switch installed in a car which did not come with one from the factory. This includes the passenger side airbag only as well.
Here's a how-to on installing a GM factory passenger side airbag disable switch in a 99' vette.
http://97vette.com/howto/airbag/index.html
Note: You must remove and replace the stock seat belt with one approved for a Corvette with disabled airbag.
