If your certificate was issued under 14 cfr part 63 and 65, it will expire March 31 2013. You can go online to request a replacement certificate by registering with the online service, or you can mail an application for a replacement of lost, destroyed, or paper airman certificate, along with a check or money order for two dollars. Here's the address: Federal Aviation Administration, Airman Certification Branch - AFS-760, P. O. Box 25082, Oklahoma City, OK. 73125-0082.
Per FAR 65.15 your A&P is effective until it is surrendered, suspended, or revoked. However, if you have the old paper style certificate then you are required to get it replaced with the new style plastic card certificates by March of 2013 or your A&P will become ineffective. You may order your new certificate on the FAA.gov website for a fee of $2.00.