Here are a couple of good sites for learning about Sharepoint 2003 customization:
About Richard Hundhausen
Richard is the president of Accentient, a company that helps software development teams understand and leverage Microsoft's ALM tools and Scrum. He has over 30 years of software development experience and over 20 years of training experience. Richard is a Microsoft Regional Director, a Visual Studio ALM MVP, a certified Professional Scrum Trainer, and author of Professional Scrum Development with Microsoft Visual Studio by Microsoft Press.