It looks like someone took the time to write an EventGhost plugin for the ISY-26 INSTEON controller by Universal Devices. EventGhost is a very stable Windows based automation package. While it isn't focused on home automation, it does have support for some of the popular IR interfaces, and is extremely flexible/powerful. I personally use EventGhost to manage some tasks from my SageTV interface (and if you use this plugin, you could probably control your lights through SageTV now). Follow the link below for more information.
EventGhost ISY-26 plugin
EventGhost ISY-26 plugin