Modern Linux is not at all that different from any other OS as far as user interface. In fact, a recent test study where some collage students took a bunch of laptops int a retirement home, half windows and half Ubuntu Linux, they found that the Linux machines were reported easier to use with people that have never used a computer before. On a side note, I've been using Linux for my day to day computing sense ~1998.
LinuxCNC, maybe a bit more to learn but you don't need to learn it ALL at once. Get the basics up and running and expand your knowledge base from there as needed. If you want to try out Linux, just download and burn a distro that has a live CD/DVD and check it out. LinuxCNC offers a Live CD so you don't have to install anything, just run it from the CD, though booting is a bit slow due to the data transfer rate of the CD ROM drive. If you like it, then you can chose to install it. You can install dual boot on the same drive if there is room, or dual boot from another hard drive or install as stand alone. You can go here -
http://www.linuxcnc.org/index.php/english/download - and get the Linux CNC image to burn on a DVD so you can test it out and install if you want to.
Mark