Use RealVNC instead
Hey Tom, I wanted to do the exact same thing a few months back. What I had to do in the end was download RealVNC for the PC (which is free) and Chicken of the VNC for the Mac. I set it up and it works flawlessly! The image is a little laggey because I use the wireless connection on my mac, but it still works.
An even better solution (and the one that I use now) is to run RealVNC on the PC the same way, and then use a program call X to X on the Mac which lets me move my mouse off of my Mac desktop, right on to the PC desktop (I have two monitors side by side). It works a lot like synergy, but I could never get synergy to work properly. Hope this helps.
Sorry for not posting any links, but if you do a google search for any of those programs they will be in the top few listings.