Identify which G4

Hi-

Use this document:
http://support.apple.com/kb/HT3082

And/or this document:
http://support.apple.com/kb/TA25585?viewlocale=en_US

They tried to upgrade the OS to 10.5 and got a message that there wasn't enough memory.

Leopard needs 512MB of RAM, and min 867MHz CPU.

The CD is stuck in the drive.

Force quit, and hold the mouse button on restart to eject.

If you would like to have more information on your Macintosh (model, date of production, etc) then enter your serial number at this site. Information, based on the serial number, will be shown. http://www.chipmunk.nl/klantenservice/applemodel.html

Look at these links.

Power Mac G4 guide
http://reviews.ebay.com/Power-Mac-G4-guide_W0QQugidZ10000000001399492

Power Mac G4: How to Differentiate Between Models
http://docs.info.apple.com/article.html?artnum=58418

Power Mac G4: How to Differentiate Between Models (Part 2)
http://docs.info.apple.com/article.html?artnum=42739

Does the Mac meet the *Mac OS X 10.5 Leopard installation system requirements*
http://support.apple.com/kb/TA24950

 Cheers, Tom 😉

How can I identify which G4 this really is?

As you see from the previous posts, there are many ways. Here's one more. Look at the tag with the bar code, on the back of the computer.