I saw this post today about how to build Universal Binaries with OS X 10.4 for PPC and x86 and immediately had to try it out with PHP :)

$ CFLAGS="-isysroot /Developer/SDKs/MacOSX10.4u.sdk -Wl,-syslibroot,/Developer/SDKs/MacOSX10.4u.sdk -arch i386 -arch ppc" ./configure
$ make
$ /usr/bin/file sapi/cli/php
sapi/cli/php: Mach-O fat file with 2 architectures
sapi/cli/php (for architecture i386):   Mach-O executable i386
sapi/cli/php (for architecture ppc):    Mach-O executable ppc

It compiled and linked just fine, if it actually does work on a x86 box, I don't know. Looks like I'll know in a year or so. I'm not gonna pay 999$ just to find that out ;)

If you want to try it out by yourself, you need XCode 2.1 and the 10.4u SDK installed. The SDK isn't installed by default (at least not on my box), you have to choose it during the installation process of XCode 2.1 (which you can download on the Apple Developer Website, if you are ADC member, but that can be obtained for free)