Step one, Download Linux off of a friend's computer (you'll probably want Fedora, since it has SELinux and can control what is installed) burn it onto a DVD;
Step two, Boot off the DVD and install Fedora Linux. Follow the onscreen instructions. (encrypt your home directory and remember your password (probably would want to make it longer than ten characters with numbers, letters, and symbols)
Step three, Install any drivers that are not there (if you have an ATI card and Intel HD Graphics, disable the ATI card off the BIOS and use the Integrated graphics)
Step four, Update the system.
Step five, Set Up SELinux so that your dad can't install anything without your password.
Set six, check regularly for keyloggers, trojans, and backdoors that your dad might have installed on your system.
Step seven, change your password every three weeks to throw your dad off if he has somehow gotten the password.
Step eight, Perform a Reinstall with the latest Fedora (or other OS) every six months. (this will get rid of any software that has slipped your mind.
Best way to browse the web is with TOR, that way, everything is encrypted so if your dad has router monitoring you can get around it.