Q: how can I install leopard without a working odd?

You cannot use your Intel Mac to install OS X on a PPC Mac. Replace the optical drive or clone the DVD to an 8 GB or larger USB flash drive. The flash drive must first be partitioned APT and formatted Mac OS Extended, Journaled.

Clone using Restore Option of Disk Utility

1. Open Disk Utility from the Utilities folder.
2. Select the destination volume from the left side list.
3. Click on the Restore tab in the DU main window.
4. Check the box labeled Erase destination.
5. Select the destination volume from the left side list and drag it to the Destination entry field.
6. Select the source volume from the left side list and drag it to the Source entry field.
7. Double-check you got it right, then click on the Restore button.

Destination means the USB flash drive. Source means the Leopard DVD.

Drive Preparation

1. Open Disk Utility in your Utilities folder.

2. After DU loads select your hard drive (this is the entry with the mfgr.'s ID and size) from the left side list. Click on the Partition tab in the DU main window.

3. Under the Volume Scheme heading set the number of partitions from the drop down menu to one. Click on the Options button, set the partition scheme to GUID then click on the OK button. Set the format type to Mac OS Extended (Journaled.) Click on the Partition button and wait until the process has completed.

4. Select the volume you just created (this is the sub-entry under the drive entry) from the left side list. Click on the Erase tab in the DU main window.

5. Set the format type to Mac OS Extended (Journaled.) Click on the Security button, check the button for Zero Data and click on OK to return to the Erase window.

6. Click on the Erase button. The format process can take up to several hours depending upon the drive size.

GUID is for IntelMacs... APM, Apple Partition Map is for PPC Macs. An IntelMac can read or even boot from an APM Partitioned drive with the right OSX on it, but APM can't be used to install OSX on IntelMacs, or do Firmware updates... but they can run just fine from them.

For a PPC Mac you need to partition using APT, not GUID. The latter is exclusively for Intel Macs. The USB flash drive installer can be used exactly as you would use the DVD. You would boot from it by restarting the computer and after the chime press and hold down the OPTION key until the boot manager appears. Select the icon for the USB flash drive and click on the arrow button to the right.

Replace your PRAM battery.  That often is the fault of non-working optical drive on any machine that is older than 4 years old.  That's all of $15.  For the iMac G5, I think it is a CR 2032 model, but you can find take apart instructions online that might help you find which one it is.  Radio Shack carries them.

Note when migrating from PowerPC to Intel Macs see this tip:

https://discussions.apple.com/docs/DOC-2295

If you are saving for a 2012 iMac, which technically doesn't exist yet, it likely won't support 10.6.8 or Rosetta.  If you are buying a new one before the 2012 iMac is released, you may still be able to call AppleCare for the original 10.6.7 or 10.6.8 installer discs which still support Rosetta.  Without Rosetta most of your applications won't work on the new Mac, and you'll have to save for all new upgrades to Universal or Intel versions of your applications.  Unless you are certain you have all Universal applications, you may be better off getting a used or refurbished pre-July 20, 2011 Mac*:

http://www.macmaps.com/usedrefurbished.html

This will save you the trouble of having to upgrade the applications until you are ready to install 10.7 which doesn't have Rosetta.