I just went through this exact problem myself! I have a dual monitor Windows 7 desktop (one 37" tv and one 20" monitor) and a Windows 7 laptop. I wanted to share the desktop's keyboard and mouse with the laptop. I tried using Synergy, but it did not work at all. Then, I tried Input Director (www.inputdirector.com) and it worked great.
One thing that I would recommend is to uninstall Synergy before trying to use Input Director. I did not do this, and as a result my keyboard and mouse were experiencing major problems, even on the master computer.
On a side note, if you are using a Microsoft Touch Mouse, the normal scrolling functions will work on whichever computer the cursor is present on, but two-finger and three-finger touch motions will be always be followed by the master computer even if the cursor is present on the slave desktop.