Admin stuff
 

I wanted to know how I could block a user's usage of the internet. I am the admin, and I want to know how I can activate and deactivate a user's internet usage at will...

and can you run windows virtually from windows???

be more specific, because if your computer doesn't act as a router you can't do anything
but i assume your linux box is a router; if so learn iptables.

Can you not stop users accessing things like the modem, or services such as pppd? :confused:

Yeah, I don't consider that you can want to block the internet for the users of the same machine...
So, be more specific...

I mean cant you set the modem to be owned by a group and only add selected users to it, so only they can use the device to go online?
You should be able to log their actions too, but I dunno about limiting their time online etc.

Btw, do you mean run some Linux apps in Microsoft Windows?

Learn about using groups. You can change permissions on certain
commands so only members of a specific group can run those
commands. Then you just remove any users that don't have
permission from the group.

man group