The PowerPC and Intel Macs are totally different architectures, so you are correct, you could only really emulate a PowerPC install on an intel machine, versus virtualize Windows/Mac OS/Linux on a intel machine.
There are some PowerPC emulators, but the one I know of for OS X would be PearPC. I have used PearPC a very long time ago, and don't know how well these work on newer machines.
Up until Lion however, at least PowerPC software was emulated using Rosetta. This was dropped in Lion though.
If you really do need a PowerPC machine, for dedicated work, I would personally buy a used older machine from ebay, which would be rather inexpensive depending on what kind of power you need.
Note: Removed iEmulator because its made more for emulating windows or linux on a intel OR PPC mac.