Updated Question:
I can't restart from the installation disc.
Despite holding down the C key and restarting, it bypasses this and goes straight to the 'insert name and password' display, which is the root cause of the problem as I want to change to a name & password of my choice.
To reiterate, I'd installed Leopard on my Mac G4. However when it got to the display requiring insertion of Name and Password which I thought was correct, it appears it wasn't. So I held down the C key and restarted from the Leopard installation disc. There I pulled down Utilities and changed the name and password. I then restarted to open up in the Hard Drive and again the display appeared to insert Name and Password which I did from the ones I'd changed to. This failed.
Again now when I attempt to restart holding down the C key to restart from the Leopard installation disc, it merely restarts and returns to the Name & Password display again. I've tried repeatedly, holding down S, Option, etc and all sorts of combinations to no avail. The system simply will not recognise startup holding down the C key to access the installation disc!
Can you please please help and advise a way out of this? Even a failsafe name and password which will be accepted would solve this too. Thank you.
You didn't need to start a new question. You could have responded to your previous question. The response (and help) remains the same, but this article should be more relevant, I think.
http://support.apple.com/kb/TS1278
If you are having problems booting to the same disk, try carefully wiping the bottom surface of your Leopard DVD. No fingerprints, smudges, or scratches.
Insert the DVD, restart, and hold the Option key. Do you get the screen that shows 2 arrow icons ( 1 straight, and one curly?), then shows your hard drive name? This same Option boot screen should show your Leopard (or Mac OS X 10.5) as an additional icon. _Wait_ for that icon, then wait for your mouse cursor to return to an arrow, and select the Mac OS X icon, then click on the right-facing arrow (the straight one). You should then boot to the installer DVD, and you can continue on with the tips from the article. If the MacOS X icon never appears, then your drive might be faulty, or your installer DVD could be bad.
Are you using the original Apple keyboard for this install?