What is the key difference between windows file protection used in XP and Windows Resource Protection used in Vista?

Windows File Protection (WFP) is a service of XP which protects important system files and other files crucial to the operation of Windows.

Windows Resource Protection (WRP) is the WFP replacement new in Vista. The amount of protected files is drastically increased and protection is extended to registry keys. Vista does this by using Access Control Lists (ACLs) and limiting changes to protected files to one program: TrustedInstaller.exe.

Administrators also have more limited control over changes in system files and registry keys: they no longer have default access; they must first change the ACL entry before access is granted to sensitive system files or registry keys.