Please Help Me With Some Api Codes

1. API to shut down the computer
2. Internet timer for Windows XP
3. API to prevent a user from changing the existing IP address (Better if i can get an API which hides the LAN connection on the taskbar)
4. API (for my internet cafe program)which determines the number of users browsing the Internet at a particular time
5. API or VBcode(I want to have a close button on the form) for disabling the close button on a form.
6. A simple VBcode which converts the difference two times(t1 and t2) and outputs the result in hours, minutes and seconds.

Thank you

This could be a startin point (but I could test it only on win2k)