XP Pro User Accounts

Hello to all.
I will thank any help or direction you may reply.

I have Windows XP Pro, and I want the following accounts set. It's a
computer for Home (Family) use, but if you can help me...

Account - "User0" - Administrator - Installations Rights
Account - "User1" - Installations Rights
Account - "User2" - Installations Rights
Account - "User3" - Installations Rights
Account - "User4" - No installations Rights

Where:
* "User0" can Install any program and this program is available to every
user;
* "User1", "User2","User3" Install any program but only them can use it
(only available on their own login);
* "User4" is not allowed to install anything;
* All users use the same "My Documents" folder. [if possible, the same
"Program Files" folder]

Must not be so complicated. But I became a little confused when I saw so
much users (Admin, Help Assistant, ASPNET, Guest, "MyAccount",
Support_388945a0 (what is this last account?)); and so much groups (Admin,
Duplicators, Guests, Net Config Operators, Copy Operators, Users, Adv Users,
Remote Users, HelpServicesGroup). I have only one accout enabled and one
disabled, as of now. How come so much groups? and accounts?

Thanks in Advance, I hope it was not too long a post.

If needed, I can format everything and ReInstall from the (Original) XP Pro
Disc

Sami