To prevent certain users from launching the app without a password indicates you want to be able to stop certain people from internet browsing.
Definately upgrade to W2k or XP.
You could then allow / restrict access to files / folders by account name, etc.
You have an Internet User policy in place? If this is a businss then you should consider implementing one as part of HR responsibility so that if a user is caught viewing something they shouldn't, they have already been warned as to what is acceptable and what is not.
Also putting in a Proxy so that the web browsing habits can be monitored, and letting users know that they can be monitored (refer User policy) could also not hurt.
let us know how u get on,
cheers