You don’t have to file an amended return or contact the IRS. The IRS will contact you by mail and ask that you send the schedule. The IRS letter will have instructions on where to mail it.
A retirement account to which up to $4,000 (or $5,000 if you are 50 or over) may be contributed for 2007, but deductions for the contribution are restricted if you are covered by a company retirement plan. Earnings accumulate tax free.