If you haven't taken much of a look at design patterns and how they can help your development life, the Singleton pattern is a good place to start. On PHPBuilder.com there's a new tutorial introducing this handy pattern and how it might fit your needs.

One of these patterns is the Singleton design pattern, which is based on the mathematical concept of a singleton (a set with a single element). [...] Sometimes the Singleton pattern can help complete important programming tasks, but only you can decide where and when it fits your needs. As a pointer, the Singleton pattern fits well when you manage a shared resource [...] because your application should have only a single instance in order to avoid conflicting requests for the same resource and to minimize performance issues.

He shows an example of how to implement it, first as a class template and then in actual use (complete with code ready to copy and paste). He also shows how you can use the singleton pattern to act as a frontend to other classes, making a sort of polymorphism simple. Thankfully, he also explains some of the risks in using this design pattern and that "less is more".