System Administration problems

[Tom Vawter]

I have a dual boot, Feisty and Mac OS X.  I wanted file sharing to work 
better.  So, I stupidly changed my Ubuntu username to match my Mac 
username - yes, I know they should have already been the same.  I did 
this in System Administration: Users and Groups.
 
The result was that I lost more than half of the items in System 
Administration including Users and Groups and Networking.
I only have left Keyring Manager, Network Tools, Printing, System Log, 
System Manager and Update Manager.

Is there a way to restore all the items in System Administration?

Thanks for your help
tom