I am running Soft Windows 98 5.0.9 on top of Mac OS 9 on top of Mac OS X with no problems. Running on dual 450 with 256 MB RAM. I thought for sure when I did this it would crash or at least run Windows so slow that it would be unusable. I think Softwindows may even be running just a little faster this way. Not that I want to run windows but if anything could kill your system it's running windows on it.
Mac OS X rocks!
Mac OS X rocks!