I went with deskcnc and am 100% happy with it. Has been running flawlessly on a vista machine with a 12+ year old serial pci card for several years.

The gui is outdated, and it does have some bugs, but for the most part it just works. They are working on a new update that is supposed to be huge.

I can do cad, email, surf the Web, watch YouTube vids etc while the machine is running and it doesn't skip a beat.