It took a little work to get them going, but it was well worth it. Basically, I query Xively for the last value, then give it to the gauge to display. Here's the current (a minute ago) temperature at my house in the Arizona, USA desert.
There's too much up there to try and explain each item; this blog post would go on forever. However, there's lots of documentation on the web that can explain what I did and the SteelSeries library has enough in it to get you started there.
Good luck and have fun with it. I'll be showing how I use the Google Graph API in an upcoming post as well.