You will definitely experience some water retention from using creatine. A gain in bodyweight of 2 lbs' in one week though is normal even if you were not using creatine so I wouldn't be singing its' praises just yet after only one week.
One misconception about creatine is the belief that by taking it, it is solely responsible for adding muscle mass. When you perform an action such as lifting a weight or sprinting, your body needs a very quick response supply of energy. This energy comes from a molecule called Adenosine Triphosphate (ATP for short) when it is transformed into ADP (Adenosine diphosphate). Your body doesn't have an endless supply of ATP and so you are only able to exert yourself for a short period of time. When Creatine Phosphate is introduced into your body in the form of a supplement, it transforms the ADP back into ATP and thus provides you with an additional energy source. This additional energy source, now available, allows you to push your workouts further and make gains which you normally wouldn't have been able to achieve. But, it is also dependant on you having a solid workout routine in place and a sufficient nutritional intake. Without these two, the use of creatine will not accomplish anything.
Creatine, in whatever form, will only assist you in pushing yourself further and any gains you make will be from this aspect.