lipo (aptly named) is a utility that manipulates universal binaries in Mac OS X. A lot of (almost all) programs these days ship, or download as “Universal”, meaning they have binary code that both the powerpc and the intel chips can understand. But since you probably don’t care about one of the two, you want to use lipo to “thin” down your binaries.
For example if you wanted to thin the “Stickies” application to only contain intel (i386) code:
cd /Applications lipo Stickies.app/Contents/MacOS/Stickies -thin i386 -output Stickies.app/Contents/MacOS/Stickies.i386 cd Stickies.app/Contents/MacOS/ rm Stickies mv Stickies.i386 Stickies