How do install Leopard from intel to ppc by Firewire?

I believe you need a similar platform, Intel or PPC on both ends.
The DVD has both PPC and Intel installs on it and it is confused they way you are doing it.
You might look into an external DVD drive or perhaps create a .dmg of the DVD and put it on an external HD on the PPC.

The Digital Audio PowerPC Mac is not compatible with Leopard. It is under the minimum 867 Mhz G4 built-in processor power (processor upgrades do NOT count). Has nothing to do with the built-in drive of the PowerPC Mac. There are faster G4s which are compatible. While there are ways of circumventing this restriction, the loss you get is in stability, and possibility for further updates. 10.4.11 was released yesterday, and you may want to consider that instead. See my upgrade FAQ* for other considerations:

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

- * Links to my pages may give me compensation.

Message was edited by: a brody

The issue isn't just the CPU speed, but you are also running on a slower bus and slower memory as well. CPU upgrades do not count; the OS isn't intended to run on a pre-867MHz model, not just a slower CPU.

I'm not commenting on whether the type of Mac is compatible with the Leopard install.

I'll offer suggestion for the firewire install. The objective is to take the Leopard DVD and transfer in some way to a firewire drive to be able to boot a PPC Mac and complete a Leopard install to the PPC Mac.

How? Take a firewire external drive and partition it in two. One for your data and the other (7.2 gigs) max, for the ability to restore the Leopard DVD to that smaller partition. Once restored you'll be able to boot(using system startup control panel) and install Leopard to a PPC Mac.
The rule to follow is to use APM ie Apple Partition Map to boot PPC Macs. GUID mapping is for intel Macs. You use options within Disk Utility ti select which way to go. You cannot have both on one firewire hard drive. I use two firewire hard drives: one APM and the other GUID.

How to setup the small partition? Connect firewire drive to your PPC Mac. Open disk utility. Create your two partitions(remember when you do this the drive is formatted and all data is gone, so backup first). Remember to use option and select APM, although on a PPC Mac it should be by default and ditto if on an intel Mac for GUID. Once the partitioning is complete, select Restore and while using the left hand column(just read the instruction in the disk utility window) and assuming you now have the Leopard DVD on the desktop , drag the install OSX section from the left hand column to "source" and then drag the Leopard small partition from the left hand column to "destination." Wait 20 minutes and you are completed. Now you can boot from the firewire drive and install Leopard to a PPC Mac.

http://docs.info.apple.com/article.html?artnum=106163

Says "Computers with processor upgrade cards are not supported with Mac OS X. Although Mac OS X may install and appear to work normally on some computers with third-party microprocessor upgrade cards, Apple does not provide technical support or assistance for Mac OS X when used in this way. Contact the manufacturer of your microprocessor upgrade card for support information. "