ASP.Net Tutorials: Creating a Layout Using Master Pages
Just as Themes and Skins allow you to factor out style definitions from your page code and maintain them in a common file, Master Pages do the same for page layout.
Customizing and Managing Your Site's Appearance
When a page that uses a master page (i.e., a content page) is requested, ASP.NET merges the content page and master page together (assuming of course that both have already been compiled).
Developer.com
Contains resources, tools, articles, discussion areas, and events of interest to Internet/intranet developers. Directories include: ActiveX, Java, JavaBeans, JavaScript, Microsoft and .NET, open source and VRML.
Webopedia's "Did You Know...?" Section
Use this Webopedia knowledge section for an in-depth overview of specific technologies and occurrences in the areas of Computer Science, The Internet, and Computer Hardware and Software.