Wordpress Gravity Forms Help

Hi! I am looking for a Wordpress expert who has a complete understand of and experience with Gravity Forms. I've started creating a form which has several conditional options but I can't get it to work the way I want. Basically I want it to begin by asking people if they are already a member on the site, if they are already a member then it should prompt them to login and if they are not then the first part of the form will require them to enter their personal details etc. If they already have an account then there should be no need to add in their details again. I have the registered users 'add-on' so that when a person submits the form they automatically get registered on the site in the normal wordpress way (they become a subscriber) this is good but it should only happen if the user has not yet registered. The rest of the form is fairly straightforward. This is a very small job for somebody who has experience with Gravity Forms and Wordpress. I look forward to hearing from you. Thanks! Mark