If you die before your Required Beginning Date, your beneficiary must withdraw all plan proceeds by December 31st of the fifth year following your death. There is no minimumamount required each year, provided the whole account is liquidated prior to the fifth year deadline.
If you die after Required Beginning Date, your beneficiary can take withdrawals over your remaining "assumed" life expectancy obtained from the Single Life Expectancy Table. For example, if you are 73 years of age at your death in 2010, then under the IRS table, your assumed life expectancy (for a 73 year old) is 14.8 years. Your Non-Designated Beneficiary will have to take annual Required Minimum Distributions in the same manner as a Designated Beneficiary described in the previous answer, except the Initial Divisor for the first Required Minimum Distribution will be your life expectancy in the year of your death reduced by one (in our example 14.8 - 1 = 13.8) and then further reduced by one for each subsequent year.
Excerpt from The Complete Guide to Estate and Financial Planning in Turbulent Times (Collaborative Press, 2011) - Walt Dallas, Contributing Autho