It looks like all the Audiofile Engineering software (includes both Sample Manager and Wave Editor) come as Universal Binaries, which means that they can run on both PPC- and Intel- based hardware.
You don't have to buy a new Mac to take advantage of all the great OS X software out there. The majority of the software can run on dated PPC hardware.
OS X 10.4 runs great on old 'Mirror Drive Door' G4s, which you can get for a couple hundred bucks on Craigslist. OS X 10.5 runs great on the beefier G5s, which you can get for around $500. And, 10.6 is just awesome, and you can run it on a first generation Macbook, which you can get for around $500 as well.
I'd highly recommend a G5.
I know you were looking for Windows solutions, but sometimes you need both a Windows box and Mac box laying around, if you really want to take advantage of all (e.g., Foobar2000, Sample Manager, Wave Editor) that's out there...