Simplehomenet has the documentation listed for an Insteon communicating thermostat on their website.  No product yet.  There's an interesting IP thermostat from Proliphix that can be managed from a webbrowser anywhere.  Kinda pricey at smarthome:
http://www.smarthome.com/3054.html
but maybe an option.  Burying 100 feet of cable (having done it a few times) is no fun and has a low WAF if you have to route it through favorite parts of the garden.