Windows 7 is just doing its job, and there is nothing to worry about it. The memory is used by Prefetch and Superfetch, which help your common apps load faster. Should you need to run something memory intensive, like a game, the memory will be cleared of this fetched cache to make room for the running app. If your dad is the techno-geek of the family, he'd understand (hopefully) that Windows 7 isn't Windows Xp and shouldn't be treated with the same set of rules and "what's normal" ideas.
There's a saying common on other boards. If you don't want your memory used, remove it from your computer, put it in a static bag, and sit it on a shelf. If you upgraded to 4 GB, the system would go after much of that as well, and this is a good thing.