My advice is that X10 is a nice starter protocol, but not extremely reliable in the long term. There are better alternatives, albeit a bit more expensive (such as UPB and Z-Wave...stay away from Insteon). Check out some of the home automation forums for advice, and if you really get into it, I'd recommend using a system like HomeSeer as a computer-based central controller.
FYI, you would need an IR543 or something similar to interface an IR remote with the X10 protocol. The IR543 is supported by Harmony.
Insteon devices themselves are ok, but Smarthome (which started as a home automation RETAILER) developed the system and there are issues with advanced features being widely supported in premium (third-party) home automation software due to a lack of a reasonable SDK. Unless the situation has changed in the last couple months.