I don't own a pronto (I'm a Universal guy), but I do control my HTPC with my MX-810 via RF. The pronto should have an RF base station that can take the RF signals and send them to an IR receiver on your HTPC. I use a USB-UIRT for my HTPC's IR receiver. There is an IR emitter taped to the front of it, that comes from my RF base station. On the software end, I use girder. Girder then controls all of my software apps (xlobby, media portal, zoomplayer and a few others). It works well.

There is one problem that I have run into. Many remotes toggle or alternate their IR codes with successive button presses, or when a button is pressed for a long duration. This messes with girder as it wants to see the same code every time. You can assign multiple IR codes to a single girder event to help that. I find it better to use a device that simply does not alternate codes. I can't remember the device I'm using as my HTPC device, but I think it's a panasonic or pioneer dvd player. I still have some problems with girder getting random codes, but it does work pretty well over all.