For purposes of ADP testing, is 2000 truly a transition year with respect to the prior year and current year testing method? If we choose current year for 2000, are we locked in, so to speak? Or can we change back to prior year in 2001? I have looked at Notice 97-2, Notice 98-1, Rev Proc 99-23 and Rev Proc 2000-26 and I might as well be looking at hieroglyphics. Please help!

You can switch between prior and current until the end of the GUST remedial period. For calendar-year plans this is 12-31-2001. Whatever method you choose for 2001 constrains what you can do for 2002.