The 10.4.8 retail disc is PPC. With 10.4, if you wanted to install it on an Intel Mac, I guess you had to use the discs that came with the machine. That said, if your eMac is fast enough and you have no need for Classic, go ahead and upgrade to Leopard. Did that on one hard drive in my G4 DA. Works nicely. I still have 10.4.11 on the other drives, though, since there are times when I want to run Classic apps without rebooting into 9.2.2.
-J
-J