Restricting types of files that can be attached to a record

Does anyone know how to restrict the type of files that can be attached/linked to a record? I am using an Access database, and I would like to restrict (not allow) attachments with the following extensions .bmp .xls .htm and .txt. I would allow .jpg .doc and .pdf files. Would this be done in the Access Database itself or is this something that is done in ASPRunnerPro using scripts?