mike,
One of the easiest methods to get from CDG to the Rue Cler area is to take the RER "B" line to Gare du Nord, and then connect to the Metro. You could also transfer at Chatelet-les-Halles but that's a larger station so might be a bit more confusing. You can buy RER tickets at CDG either from ticket machines (however a "chip" credit card would be needed) or from the ticket office (at times long queues though). For a more detailed look at that option, have a look at parisbytrain.com as it's well explained there.
You could also consider one of the Shuttle firms or the Air France or Roissy Bus, which will drop you in central Paris close to a Metro stop. From there you could take a Taxi to your Hotel (I think that's the method mentioned on your Hotel's web site). Your Hotel appears to close to the Ecole Militaire Metro stop, so that's the method I use. Depending on what time your flight arrrives, the Metro may be busy and you'll be tired and hauling your luggage, so something else to consider.
I wouldn't recommend a Taxi as they tend to be expensive and of course if there are "traffic issues" it could cost you a fortune!
I'd highly recommend packing along a copy of the Paris or France Guidebooks, as the transportation options are all well explained. The Guidebooks are also a great reference source while travelling.
Good luck and happy travels!