Microsoft has forked Windows common controls into two separate versions. Version 5 is available on all Windows versions from Windows 95 or later; it displays controls using a "3D chiseled" look. Version 6 became available with Windows XP. Under version 6, controls are rendered by a theme engine which matches the current Windows XP theme. If the user changes the theme, version 6 common controls will match the new theme automatically. You don't need to recompile the application. 

The VCL can now accommodate both types of common controls. CodeGear has added a number of components to the VCL to handle common control issues automatically and transparently. These components will be present in any VCL application you build. By default, any VCL applications will display version 5 common controls. To display version 6 controls, you (or your application's users) must add a manifest file to your application. 

A manifest file contains an XML list of dependencies for your application. The file itself shares the name of your application, with ".manifest" appended to the end. For example, if your project creates Project1.exe as its executable, its manifest file should be named Project1.exe.manifest. Here is an example of a manifest file:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<assembly xmlns="urn:schemas-microsoft-com:asm.v1" manifestVersion="1.0">
<assemblyIdentity
version="1.0.0.0"
processorArchitecture="X86"
name="CompanyName.ProductName.YourApp"
type="win32"
/>
<description>Your application description here.</description>
<dependency>
<dependentAssembly>
<assemblyIdentity
type="win32"
name="Microsoft.Windows.Common-Controls"
version="6.0.0.0"
processorArchitecture="X86"
publicKeyToken="6595b64144ccf1df"
language="*"
/>
</dependentAssembly>
</dependency>
</assembly>

Use the example above to create a manifest file for your application. If you place your manifest file in the same directory as your application, its controls will be rendered using the common controls version 6 theme engine. Your application now supports Windows XP themes. 

For more information on Windows XP common controls, themes, and manifest files, consult Microsoft's online documentation.