Is it possible to get Java 6 running on a Mac PowerPC with Mac OS X 10.4? AFAIK SoyLatte is only available for Intel processors.
Someone yesterday recommended SoyLatte for PPC (http://stackoverflow.com/questions/607945/installing-java-6-on-mac-os/607966#607966), and in fact these instructions seem to support his theory (read the comments where someone claims it works on his PPC): http://blog.adsdevshop.com/2008/02/26/installing-the-jdk-16-on-mac-os-x/
YMMV :-) Or try building from source. Again, YMMV :-)
Note that in addition to not working on PPC, Apple's Java6 does not work on 32 bit Intel either. And there are other restrictions for the new Java6, leading to opinions such as this.
The only Java 6 for PowerPC I have seen is for Linux:
http://www.ibm.com/developerworks/java/jdk/linux/download.html
I am afraid you will have to stay with Java 5 on Mac OS X on PowerPC.
As of December 2009, a beta of OpenJDK 7 for OS X 10.5 PPC is available at http://landonf.bikemonkey.org/static/soylatte/ -- haven't tried it, and it's not quite what you were after, but it's the first I've seen so far of Java >=6 on any PPC OS X version! More details at http://landonf.bikemonkey.org/2009/12/index.html .