When you navigate to the User Profiles dialog at Control Panel / System / Advanced / Settings (under User Profiles), and select a user profile to copy, the Copy To button for that that profile is not available.
This behavior occurs if the profile that you wish to copy has been used since the last restart, even if only by Scheduled Tasks.
To workaround this behavior, restart the computer, insuring that the profile you wish to copy is NOT used to logon the console, over the network, or by the task scheduler.
Another possibility is Microsoft Knowledge Base Article 894232, entitled 'The "Copy To" command is not available when you try to copy user profiles on a Windows XP-based computer', which contains the following description:
Fixes an issue in Windows XP where user profiles are not unloaded and where the "Copy To" command button in the "User Profiles" dialog box is not available. Therefore, you cannot copy profiles.