If you wish to copy themes from one Windows 7 system to another, copy the contents of
\Users\Username\AppData\Local\Microsoft\Windows\Themes, where Username is the account name for the account from which you wish to copy the themes. If the new system doesn't have a
\Users\Username\AppData\Local\Microsoft\Windows\directory, because no themes have been added, just copy the
Themesdirectory itself from the source system to the destination system. Afterwards, on the destination system, you can right-click on an empty area of the desktop, select Personalize, then select the theme you wish to use.