Bryan H:
If you install an application for exactly one users, like MJ does, the directories and files created by this installation are getting the ownership of the current loged in user. If you want to reinstall MJ for different users, you have to give them the right to modify and delete the files. So go to the security-options of this (installation!) folder (it is somewhere below the properties box accessed by right mousebutton) and check, if you gave all users (or the once in question here) the full access rights. This should solve problem number one. Maybe even give, for testing purposes, everyone access to everything _in this folder_ (and _for_ this folder). You may even have to give full access to the "program files"-folder. After installation you may take this right away again (but not the other ones, because there is a database-file in the installation-folder, which changes).
You can check, if you did everything right, by typing "md testfolder" in the "program files"-folder in a command-line. If there is no error, you can remove the created folder by "rd testfolder" again. And you might edit a textfile in the MJ-application-folder (create one) and save it. If there is no error, you have the necessary rights. Then install with that user.
If this doesn't help, you have to check, sorry for that, that the files created by the installation in the system-directory are created using the above described rights. They have to be overwritable by all users also (by default, setup-program shouldn't try to overwrite systemfiles with the same version, but you never know, right?).
The reason for all of this is the security feature of WinXP. If a setup-program doesn't recognize a multiuser environment and only installs as a single-user application, what quite much applications do, they are all installed by the rights of the person installing (because in WinXP (and 2K) this is the default). That's the reason why nobody but the admin should install software. But he has to give access to all users on the system, too. If the setup of an application creates registry-keys, they're mostly in the user-tree (that's the reason for reinstalling the application with different user-logins; many application can't handle empty reg.-settings). So there should be no problem with that. And even if it is, you may edit the security-settings for registrykeys also (but I don't think this is necessary here).
HTH,
Mirko