Don't install Media Player and you'll not have a problem on those 200 users workstations.
If you are going to be using this for LAN parties you can chose what you actually share and even associate passwords with certain files/Folders buy you'll have to individually chose what it is you want to share and not just share the entire drive or folder. So you could share all other folders in your My Documents folder but not My Music. That way at least you could prevent anyone removing or even deleting your personal music files.
I'm actually at a bit of a loss on exactly what it is that you want to do here as your question is a bit vague on what it is that you actually want to try to do. You can not have XP working as a Domain Controller or for that matter have more than 10 concurrent connections in a work-group environment and that is for the Pro version it's less for the home version which you can not join to a domain.
If these are work computers do not install Media Player it's not a standard install with XP and you need not bother to install it. If however this is for something else you'll need to set the permissions on your personal files and protect them with a password and you can use different passwords for different folders or if you are working from a Server you can configure sharing policies with different levels of passwords for different users.
If you would like to expand on your original question I might be better able to answer your question.
Col