You can't really test this stuff until Jan 1st 2000. We don't know all the risks. There is a finite speed at which one can spend money effectively. Only the Lone Ranger risks his client's safety on silver bullets. Dates on the calendar are closer than they appear.
Testing is the only insurance worth buying.
Three things are certain in life, Death, Taxes and Y2K. Y2K will pass. If you rest easy at night, you don't understand the problem. Windowing is a temporary solution. The closer the date, the higher the cost. Don't fix everything, fix everything that matters.