How do I swap admin privileges between two accounts?

Question

The original, first account on my computer is, naturally, an admin account. I normally operate in this account. How do I create a new account that becomes the sole admin, and change the original, first account to an ordinary user account? The reason for this (security is the motivation) is that I want to still use all the folders and files owned by the account that is currently admin. If I just create a new non-admin account, when logged in as the new user I have no access to my old Library, Music folder, Pictures folder, Keychains, etc. I don't want to duplicate the existing admin user folder and double its hard drive footprint. Is there a simple way to just make the current admin account a plain user and the new account the admin?
PB G4 1.33GHz 1.5GB RAM 60GB   Mac OS X (10.3.9)  

Answer 1

The original, first account on my computer is,
naturally, an admin account. I normally operate in
this account. How do I create a new account that
becomes the sole admin, and change the original,
first account to an ordinary user account? The
reason for this (security is the motivation) is that
I want to still use all the folders and files owned
by the account that is currently admin. If I just
create a new non-admin account, when logged in as the
new user I have no access to my old Library, Music
folder, Pictures folder, Keychains, etc. I don't
want to duplicate the existing admin user folder and
double its hard drive footprint. Is there a simple
way to just make the current admin account a plain
user and the new account the admin?
Yes! I just did this for the same reason. Create the new account and in System Preferences/Accounts/Security check the box at the bottom to "Allow user to administer this computer". At this point both accounts are "admin" accounts.
[I had the same problem with not being able to access some, but not all, of the folders in the original account. When logged into the original account, I went through each folder that I had no access to when running the new account and changed permissions in the Get Info window and selected "Apply to enclosed items...". to allow the new account access. (BTW, There is an Apple Tech note that says "Apply to enclosed items..." doesn't work for owners or groups.) I ran Repair Permissions many times and changed group permissions on some folders that were "admin" group. I ran Disk Repair. And after many times doing the same thing over and over, suddenly I had access to the original account folders from the new account.]
Now log into the original account and select the original account in the accounts window and then Security. Now deselect the "Allow user to administer this computer" box. This means that to administer the computer you now must be logged into the new account.
I'm still not sure which of the things I did actually made things work, but now I can access the original account files from the new account.
Good luck!