Run EXE as System

Question

Hello,
I am currently faced with a problem of running an EXE as system when the user logs in on a limited account. I am currently designing some security software and what I want it to do is load at logon immediatley before any other program. I am thinking do I need to design a system service which runs a seperate EXE or is there another way?

Its very important it loads imedatley before explorer etc because I need to make changes to system plocies such as "NoRun" etc.

Kind Regards,
Rob