Medicare beneficiaries will not be allowed to buy insurance to cover their share of prescription drug costs under the new Medicare bill to be signed on Monday by President Bush, the legislation says. Millions of Medicare beneficiaries have bought private insurance to fill gaps in Medicare. But a little-noticed provision of the legislation prohibits the sale of any Medigap policy that would help pay drug costs after Jan. 1, 2006, when the new Medicare drug benefit becomes available. This is one of many surprises awaiting beneficiaries, who will find big gaps in the drug benefit and might want private insurance...