Dave (planet10) would be the person to talk to on this, I believe.
I'm sure there are some -- whether they're free or readily available remains to be seen, of course.
You may well end up being far better off running virtualPC.
Heck, you can get a good PC for doing stuff like that for $299cdn these days (without a monitor), which might end up being the best route. For that price, I wouldn't bother with something like VirtualPC.
I am just getting into this electronics side of things, and have used two packages, Osmond, which seems basic, and EDSCad lite, which is a cut down version of an expensive but powerful commercial package.
Both have problems- mainly with parts libraries, you have to define just about any part you use apart from a 1/4w resistor, and both seem clunky to me, but as I have never used any other PCB software I don't know if this is a generic thing across platforms or not.
Both are free downloads, so I would just get them both and give them a go.
A GREAT schematic program for the MAC is 'Designworks Lite 4.0' Check it out on the web. It is a download, and in two versions. An expensive one that will give you everything, and a cheap one that draws great schematics.