If the land around the house is well drain and the house is high up, you might not need to do anything to the floor. completely seal with tape a piece of 12" by 12" plastic bag to the concrete floor. After a couple of days, lift it up. If the concrete is darker under the plastic, it means that humidity is seeping trough the floor and it is being trap under the plastic. If that is the case, there are several products that come in paint form that you can use to seal your floor. Even though you are planing to cover it up with carpet, you should look for one that is rated for use in floors. A trip to your local hardware store should provide you with brochures of several brands. Hope this helps.