You might try Wine but it isn't an emulator, since it doesn't emulate any hardware and that is a good thing. wine can be grabbedhere.
Edit:
This is assuming you are running on an Intel Mac, if you are running OSX on a PPC then you NEED an emulator(that is slow) and there I can't help you. <{POST_SNAPBACK}>
why would anybody wanna use Wine for Intel Mac, when you can just run native WindowsXP on it ?