One of my users is using Windows XP. I installed a program under administrator and it installed successfully. But under his profile it doesn't work 100% because he is under the users group on local machine. If I add him to the power users group application works 100%. Reason why it will not work successfully, is because application rights entries to the registry under HKEY_CURRENT_USER\Software area. When using users local group it does not give him access to write it on that section but using power users group it does. How do I give him access to the registry hives under his profile in order to get application to work using the users local group?

Short of putting him into a local security group (administrator or power user) i dont see how you can grant him access.

Did you change the permissions on the Program Folder? Try that first. Give Users Modify on the folder and all child objects (subfolders and files). You may not need to correct the Registry Key permissions. Life's more painless for the brainless.