Try this one :
http://www.smarthome.com/1411cu.html Is the only thing I see that can be linked to computer.
We don't have insteon here and i'm afraid is not supported right now.
But if you have such a device and documentation of how it works (what you need to send to it to do something, and what you receive from it) you can create a working pluto device by implementing it as Generic_Serial_Device.
You'll need to write small piecies of Ruby code on pluto's web interface and that's it.
For more information about GSD please search forum for GSD and Generic_Serial_Device
