When you bind a bow and start using it does that bring up your marksman skill or do you have to use a reguler bow to bring up your marksman?.

Bound bow works to build Marksman just like a physical bow.

so by conjuring a longbow and then using it. it will level up my marksman. and by conjuring the bow itself my conjuration would level up two man why haven't I ever used this in oblivion.

You also get a 10 bonus as well when ever you conjur up anything as well. At least for bought spells not sure if you get the bonus if you make a new spell.