Some beneficiaries of an IRA owner who passed away a couple years ago have been receiving the owner's RMD which was initiated before the owner's death.

Can the beneficiaries switch to the new distribution rules in calculating the RMD based on the new life expectancy talbe or must they follow the rules of the calculation prior to the recent law changes?

In another situation, an IRA owner passed away in May, 2000. The beneficiary's first MRD is due December, 2001. Can he apply the new MRD rules for that first distribution?

Assuming that the designated beneficiary(ies) is/are individual(s), then distributions for years after the year of the owners death can be determined using the beneficiary's single life expectancy. (ie the new rules) So yes, you can use the new rules in the situations you described. I'm assuming that the calculation for the year of death (2000) in your second situation was properly calculated using the OLD rules.