A few years ago, when I was just getting used to Linux, I got around the problem you're having by making 2 partitions on my hard drive; one for Linux and one for Windows.

Partitioning your hard drive basically splits it in 2 or more parts. This can allow you to install 2 operating systems which are completely separate from each other.

Unfortunately, this would probably require formatting your hard drive, which your dad may not be very keen on doing atm.