I tried in vain to enable distributed compilation in Xcode on a few Snow Leopard machines. Some searching led me to this thread.
Apparently you have to start Xcode in 32-bit mode (this is set in the Get Info window in Finder) for it to work properly.
Now it would be nice if you could use non-Macs or PPC machines as well. GCC support cross compiling so, at least in theory, it should be doable.
[crarko adds: I haven't tested this one.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=2010101510551398