Most AM radios use a built in ferrite loopstick antenna. For FM, it might have the functional equivalent of a whip antenna.
In either case, a simple inductive coupling might help. Get a length of insulated wire, and wrap, say, 10 to 20 turns around the radio, then extend the remainder of the wire (say, 10 to 20 feet) around the office wherever you can find a place for it. (Higher is better, but avoid flourescent lights). That should get you a better signal level, however it may or may not also increase the noise level. (My dad used to do this so he could hear the baseball broadcasts in his shop, deep inside the AC Spark Plug plant).
If the indoor inductive coupled antenna is not satisfactory, try one of the Terk products:
http://www.audiovox.com/webapp/wcs/stores/servlet/GenProductListCmd?type=nprev&catalogId=10001&storeId=10001&categoryId=5062&langId=-1&page=&urlString=&productId=&brand=