[X4U] Using su and sudo f rom the terminal

[Peter James]

I'm using a G5 iMac running OS X 2.4.3.
I've always understood from previous experience with Unix and Linux  
that typing su or sudo from in the terminal will allow the user to  
operate for a short period as root.  When attempting to run su that  
requires the admin password, the error message is sorry.  When  
attempting to run sudo and typing in the user password the error  
message is to the effect that my user is not a member of the sudoers  
file and that this attempt will be reported.
I have edited the sudoers file by allowing all users authority to  
use  sudo upon production of a verifiable password.
My system is set up with one user with admin privileges and one user  
without.  Can anyone give me any advise on this situation?