Jim, thanks for the input. I would prefer not to erase the whole HD. I have found that I can not boot from the optical drive in order to use the "Utilties" to change previous owner's id and password.
Could be that the CD is downlevel for your machine.
Mac will not boot from cd that contain older software than was shipped for the machine.
Try holding down the option key then power on. This brings up the startup manager. Click on your hd. Click on right arrow key.
There seems to be some sort of EFI firmware protection. If you have any knowledge on it let me know.
I think you need to type in a password when ever you boot the machine.
The iMac G5 doesn't use EFI Firmware. It's called firmware as far as I remember right now.
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Get the Mac to set up an additional administrative account. You can then change the password on your old account.
Start with your computer power off. Hold down command-s. Power on your computer.
Type in the following:
The first two commands will depend on your release of Mac OS X. Look at what is typed out in the console to determine the exact format.
# Type the follow two instructions to access the startup disk in read/write. Press return after each command.
/sbin/fsck -fy
/sbin/mount -uw /
cd /var/db
pwd
#List all files. The l is a lower case L.
ls -a
#The move command acts as a rename command in this format.
mv -i .applesetupdone .applesetupdone.old
reboot
Once you've done that the computer reboots and it's like the first time you used the machine. Your old accounts are all safe. From there you just change all other account passwords in the account preferences!!
Limnos adds detailed explainations:
http://discussions.apple.com/message.jspa?messageID=8441597#8441597
The above the idea came from a post by JoseAranda at September 9, 2006 3:48 AM
http://www.askdavetaylor.com/how_do_i_reset_my_mac_os_x_admin_root_password.html
You will need to scroll down to see this post. Search for applesetupdone
Once you have a new administrative account, you can change the password of your old administrative account
blue apple > System Preferences > Accounts
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-- You can see that it is easy to change your administrator password. You can set a firmware password that you enter before your machine will boot.
http://support.apple.com/kb/HT1352
-- For the best data security, you should use FileVault. Create a good logon password. Define and use a good backup plan. I do not recommend using FileVault unless you really need the security because it is much harder to recover your data should you have a harddrive problem and you do not have your data backed up.