The issue it seems is that the TD needs to access the Windows registry, because this is where the license is stored. If it cannot access the registry, it defaults to expired evaluation mode. In order to access the registry, the application must have "administrator level access".
With Windows Vista, even though the user account with which you login IS an administrator (if you've set Vista up this way - which most people have done), when you launch an application Vista still runs it in "user mode" - meaning it does not have administrator level access. To make things more confusing, it seems that after you install a new application, the FIRST time you run it, Vista will run it as an administrator, but subsequent runs it does not (I could be wrong about that, but that's the pattern). Therefore, one downloads the software, runs it, gets to use the evaluation mode (because it was run as an administrator), then exits the program. When they run it again the evaluation mode has expired (because this time it was run as a "user").
In fact, the evaluation mode has NOT expired, it is just that the software must be run as an administrator. If you right-click on the Tournament Director shortcut, you can select "Run as...". There you will be able to tell Windows to run the application as an administrator. You can also right-click on the shortcut and select "Properties". There you can permanently modify the shortcut to always run as an administrator.