Making web-sites scale is a non-trivial thing to do. It requires a lot of knowledge of the operating system, the web servers, databases, using php scripts and so on. However, a very simple technique is to use add a lot of caching, and wring out as much productivity and efficiency as you can out of the hardware/software.

This article describes some of these techniques and I know for sure that a bunch of them work quite well (such as the PHP-accelerator which caches compiled php files). Give it a try!

Another simpler option which lazy bums like me would prefer is to use a managed hosting solution like that of WordPress.