For the folder like C:\Prgoram files and C:\Windows, the Power User group cannot access those folders in Windows 7. Apart from taking ownership from TrustInstaller and change to local admin and grant the access right to Power User, is there any way for Power User to have access right to those two folder in Windows 7?

First off, the group name is Power Users (note: plural). If you are a member of Administrators, you need not take ownership to add Power Users group permissions (e.g., Full Control) to those folders, as far as I can see. Granting any level of user the permissions to freely access those folders goes against the very concept of UAC though. -Noel

So except for take ownership and granting right to Power Users, there is no other way for Power Users to access those two folders?

Define "access those two folders". Users have read & execute permission by default, and Power Users have no presence in the security settings for Program Files, et. al. That's just the way it is set up during Windows installation. Assuming you want write access into those folders, your question is essentially "So there's no way to get around Windows security?" Why do you want to? An entity with permission granting permission to others who need it is the right way to do it. -Noel