Rosetta is indeed an option in 10.6. If you don't have it installed, you can do it by inserting the 10.6 DVD, mounting it, and selecting Optional Installs. Alternatively, if you launch a PPC-only app, the OS will ask if you want to download and install Rosetta directly from Apple. You need to do this only once; it will work for all PPC apps thereafter.
If you're in 10.7 or later and need Rosetta, you're out of luck.