Here are two stored procedures for enabling and disabling all keys (primary and foreign) for a specified database. It makes sure the database specified is not the system databases and the users session is at the DB to have its keys enables/disabled.
For most DBAs, normalization is an understood concept, a bread and butter bit of knowledge. However, it is not at all unusual to review a database design by a development group for an OLTP (OnLine Transaction Processing) environment and find that the schema chosen is anything but properly normalized. This article by Brian Kelley will give you the core knowledge to data model.