Or he can just reinstall jj2, which I am sure he bought legally... and if not, he can try his hardest not to obtain it illegally

EDIT:
In order not to be so annoying I searched and found this at Haze's hideout:
Jazz2 Un-Install Aid

".inf file which deletes the Jazz 2 registry keys if you manually deleted Jazz 2 without using the proper uninstall program. If you did this and tried to re-install Jazz 2, an error would occur telling you Jazz 2 was already installed. This program deletes the offending registry keys so that you can re-install without any problems.

To Install: Right-click the j2_uninst.inf file and select Install from the menu. Or double click the .inf file."