This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates on-line! See this thread for details.
Yes, you can open connections to different databases using different drivers at the same time. I don't think an example is necessary; simple duplicate the code you use to connect to your database and change the parameters - done!
Class.forName() registers the forName()'s parameter class with the DriverManager once and only once; and these drivers map specific URLs onto themselves. "jdbc.drivers" system property contains them actually too.