90% of injection is done in the constructor of the class by passing in instances as interfaces. The other 10% is done primarily through a setter property and in rare cases as a param to a method.
IoC = Dependency Inversion Principal. A service locater returns the concrete instances of classes requested. The service locater is a container.
Microsoft.Practices.Unity is a popular Microsoft container and Windsor Castle is the most popular open source container.
Links to containers: