I'm not sure what "I" am. I'm not sure if I care or not. I'm not really sure what labels matter and which don't. But, I can tell you what the actual dictionary definitions are.
Transgender: An umbrella term that encompasses any and all people that do not fit the confines of a binary gender society. The fruit analogy someone put is apt. Transgender is like the category "Fruit" while Crossdressers and Transexuals are specific types of fruit.
-Crossdressers
-Transexuals
-Intersexed
In a nutshell anybody that isn't 100% physically and mentally one gender. (I will leave out Melody's rather lengthy subcategories and stick to the generic ones here)
Crossdresser: A person that wears the clothes of the opposite gender. Notice the period at the end of the sentence. It goes no deeper than that. It includes fetishistic crossdressers, and it includes anyone else that wears the clothes that are meant for the opposite of their biologic gender. Also note, nowhere in that definition is "masturbating to a pair of panties." However, if someone wears a pair of them, and then masturbates they would be a crossdresser.
Crossdressing is a VERB. It's an action. Doing something. A crossdresser, is a person doing that something. IE descriptive noun.