Parental controls

Hi. I'm a computer addict who spends every minute of pastime on sitting at a computer. I've been fighting this addiction for years trying to find a solution that's not too drastic and will help me live a normal life. When I thought everything else failed, I decided to set up the time limit using the admin account, whose password my parents know. It's proven to be foolproof so far, but there is a huge disadvantage: I'm the only one who uses this computer, yet I can't install, modify, or use so many files I need without the admin's permission. I'm trying to do more productive activities than playing games and websurfing, like learning photoshop and programming, but I can't install fonts, compile, and so forth because I don't have the admin privileges. Considering the number of things I'm asked the permission for, it's unrealistic to ask my parents to log on to the admin account everytime I need it. So my question is, is it possible to use an admin account and still force it to log off at certain times? If not, do you know of any program that can do the job?

p.s.: I expect many people to say, "go outside and do something else." It's a long story, but I'm posting here because I've already tried that, and it didn't work.

edit: sorry that I made another thread. Thank you for merging them.