Several readers have noted a new opensource project that is generating some interest.
PearPC 0.1 is an early version of a "an architecture independent PowerPC platform emulator capable of running most PowerPC operating systems". The emulator offers emulation for various PowerPC operating systems including Mac OS X 10.3 (screenshot).
According to reader reports, the application does appear to work, but is slow and clearly at an early stage of development so of limited use at this time.