Compiling programs for the PPC works already, if you’ve installed Gentoo like described in installing_gentoo. If you have another Linux distribution, then you can try the Barcelona Supercomputing Center rpm packages here. If you don’t have a PS3 yet, take a look at The Cell Simulator where you can download a Cell simulator and a cross compiler.
If you have Gentoo installed and if you want to compile programs for the SPEs, follow this howto.
Some more reads are here