I'm running a Windows 7 desktop machine (no GPS, hardwired connection) which is stationary. I'd like to set up my location so that various geolocation-enabled services can find me accurately. Is there any way to do this?
Windows 7 needs a sensor installed to provide the services (Google) with information pertinent to the service.
One such sensor is Geosense which will provide the behavior you are looking for. The sensor currently supports Google Location Services via IP/WiFi.
The framework exists within Windows 7 but it still requires 3rd party implementations which will provide the sensors and thus integration to services such as Bing/Google. Unfortunately; the developer community has been fairly slow to respond thus far.
With regard to geolocation via HTML 5; that is reliant on the browser and how they support HTML 5 and consequently geolocation. If you encountered a page written in HTML 5 leveraging the geolocation API's; the browser implementation would come into realization at that point. If the browser provided a way via browser settings to provide a fixed latitude/longitude position, that would be up to the specific browser in use.