Both Synergy and Input director work fine for me on win7 and xp machines networked together. Seeing how you have problems with both programs seeing other systems sounds like a network problem to me. Firewall, permissions, non matching workgroup names, or even some goofy router setup that's trying to route traffic to the internet and back instead of across the network. But two completely different network apps have the same network problems. My money is on the network being the problem, not the apps.

You could test it pretty easy if the systems have gigabit nic's just run a network cable from one to the other, no switch or router needed, set some static ip's and try it again.