Quota Screen To Limit HD Usage

Brand new Windows 7 user.

Two users on this new PC; myself and son.

Want to limit the amount of HD space he can use, or my 1 TB is going to be filled 100% with videos, music, etc. in short order.

So I went to the C: drive/Properties/Quota and played around with it some, but haven't actually applied it.

For me at least, it's not totally clear what happens, so would like to ask the following, please:

a. When I first got the PC a few weeks ago, I set up myself as a User.

But did not apply any Passwords or sign-in requirements for either of us..

A week or so later, I added my son's name, also, as a User.

Since there are no passwords, sign in Passwords, etc., am I considered the defacto Administrator (as I was "first") ?

b. It is not clear that if I set up a limit on this Quota option screen(s), is it applied to both of us, or just him (if I am considered the Administrator) ?

I thought that there would be some kind of screen showing both Users, and what their limits are, but apparently not ?

c. Can this be done without any Passwords, sign in Passwords, etc ?

Not too sure what else to ask.