Prevent process from kill or hide it from TaskBar

Hello.
Fist of all sorry, my English is not good.

So, I developing a delphi application, which is timer. The idea is: in one room there are 20 pcs for example. One of them is server. When user wanna use a computer, he calls to the server operator, and the server operator allows to him to use some of this 20 computers for 1 hour for example. When the time is off, the server sends signall and the client computer reboot automatic.

So here is the problem. When i run my client application, it can recieve commands from the server. I mean this time limitations. But if the client closes this application, the limits are gone. So, I disable the Close button of the form, but process can still be killet by TM of Windows 7. And this is not good. Can someone give me an idea, how to hide it or to prevent process kill?
I am using Delphi 7

P.S. I know that this infomation can be used for... not good ideas, so if someone has an idea, send it at pm, please.
Thank you for the help, and I hope you can understand what i have wrote ;D

Instead of running an application, which obviously the use can easily terminate, create a Windows Service Application. Here is a tutorial on how to do so,

http://www.tolderlund.eu/delphi/service/service.htm

Also, a service has two properties that you can set:

AllowPause Boolean
AllowStop Boolean

Set both to False, and it will be more difficult for your user to kill the service (but not impossible)

Thank you. I`ll try tonight and I`ll report the result