Q: need disk to reset G5 computer

It will be better and much cheaper to find the disc.

You will either need a machine specific, gray disc that shipped with the machine, or, a retail version of Leopard.

Machine specific discs are iffy at best, unless you happen to have a record of the disc version that you had.

Retail discs are available on eBay, but are costly.

Let's try and reset your main password without a disc. Follow these instructions:

http://gigaom.com/apple/reset-os-x-password-without-an-os-x-cd/

Another take with other options:

http://www.macyourself.com/2009/08/03/how-to-reset-your-mac-os-x-password-withou t-an-installer-disc/

You can call Apple Customer Support 1-800-767-2775, provide the Serial Number and specifications of the Mac, and for a fee, a replacement set of system discs (if available), can be ordered.

However, the discs will be for the original version of OS, that was pre-installed, when the Mac was manufactured.

 Cheers, Tom