Ron, your mounting setup looks identical to mine! This is my 2nd riding season with that setup and it has worked great.
If your GPS didn't come with a disc for the MapSource software, you should be able to download it from the Garmin website once the device is registred. You can create routes in Mapsource at least a couple of ways. With the Route tool you can just click on different points and it creates a route to join those points. Or you can identify a number of waypoints, then select them and create a route using the selected points.
Once you have a route(s), plug in your GPS with the USB cable and you can transfer the routes from Mapsource to the GPS.
Another option is Microsoft Streets & Trips. I downloaded a trial version a couple of months after I got my GPS, and never went back to Mapsource. To me, the map is much easier to use, and the software seems more intuitive. It also can optimize a route, which is great if you're trying to hit several locations in one ride and you want to find a route that minimizes the time. It is a few more steps to get from route in S&T to a route in your GPS, though.
Keith