Vista (and 7) protects the files and folders in c:\Program Files. Changes that are made there are done in a non-permanent way or simply refused. It was intended to prevent malware getting a hold on your system. But SH3 is to old to work around it by itself. If you look in the Control Panel under Programs and Features you can check the list of installed programs if it really did stick.
A rather simple solution is to not install the game in there (Program Files). Just give a different install folder like "c:\Games\Silent Hunter 3" when it asks for the installation folder. You still have to use an account with administrator privilege. You always need that to install or patch things if it comes as an installer package (.msi or like setup.exe). Even the GWX mod installer if you ever decide to do it. You'll have to ask that tech-guy what account he used to install it, and the password that goes with it if you don't know it. Even if you do not have enough computer knowledge I advice you still demand to know the account and password as without it your hands are coughed forever with that system. Even to do something as simple as setting the system date and time.
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