Code Section 409(o)(1)© provides that the plan must provide that unless the participant elects otherwise, the distribution of the participants' accounts will be in substantilly equal period payments over a period of 5 years (extended for large account balances). Does this mean that the plan has to offer installments? Does this mean that a plan can't just offer a single sum payment option (permitting distribution of stock or cash at the election of the participant)?

IRC section 409(o)(1)© requires a distribution period that is generally "not longer than" five years. A single sum payment would satisfy that requirement.