We use terminal services for our remote users. How can I configure two internet services to where when one goes we don't lose connection.

Right now we have 20 Mb cable and it seems to go down once a week or so.  When they do all of our remote users are dead in the water.  I know I can get a DSL account and use it as a backup, but whenever the router switches over to the DSL connection the IP address would change which would kick off all the remote users.  Is there a way to create a seamless connection to whereas the router switches over to the DSL the remote users would continue to work.