Ok, well some experimentation with several different computers suggests that the reason it runs in slow motion on the Windows computer is that it is consistently maxing out the CPU. Given the published tech requirements I thought a single core 1.6Ghz laptop with 2G of RAM would do it but it's really not sufficient, at least running a lot of channels at the same time. That's clear when you run the system monitor and watch CPU levels.
Running it on the much more powerful macbook pro seems to only require about 15-30% and it runs flawlessly. 2.5Ghz dual core, 4G RAM, no problem. I'm betting it I ran it on a sufficiently powerful windows computer it would be fine.
So maybe the tech specs should reflect that you need a considerably more powerful computer than suggested unless you only plan on running a few channels of DMX without a lot of scene changes etc