Limit Max Volume

I have an issue I am hoping someone can help me with. I recently purchased an Intel Mac Mini, and need some help.

My 3 year old son has become comfortable enough with the computer that he can log himself in, and launch Firefox to go to his kid friendly websites. The problem I have is that he has also figured out how to turn the volume up using the keyboard. Since he usually wears headphones we don't notice right away that he has done this.

What I am hoping to be able to do is set the default max volume for the system (something similar to what Apple did with the iPod), or at the very least disable the volume control keys on the keyboard.

If anyone can I would greatly appreciate it. I have done quite a bit of digging around and haven't found a suitable solution yet.

Volume fix

I'd just dedicate a set of headphones to your child's use, then cut the headphone cord about 4 inches from the plug and solder in a simple resister.
What size of 1/4 watt resister to use is up to you as that will set the volume permanently. Try different R.Shack sizes/volumes before soldering it in.
Almost forgot- slide a piece of heat shrink tubing onto the cord before adding the resister and run a hot part of your soldering gun over the heat shrink (after the solder is cool) until the tubing seals itself on.

Ok, I have to admit that while trying to troubleshoot this I never actually thought to modify the headphones to limit the volume. I am going to have to look into this since I have not done anything with electronics in a very long time, and don't remember most of what I once knew. I will also admit that this response is far more clever than anything I had expected, and am quite pleased to have gotten it. I can't pass up a chance to hack on some hardware.

While I am playing with modifying the headphones themselves if anyone has a software solution that would work I would definitely appreciate it.

Thanks!

Edit his account, using System Preferences>Accounts, so that he can not change system preferences.

I dont' know if this disables the ability to turn up/down the volume with the keys, though, and I can't test it since I'm at work (Windows).

I'll give it a go when I get home.