Hep with a tough form/registered user information

hey people, im here @ the office and i was assigned a new site to work on… i never had to do something like this before, but obviously, i know it can be done.

its a website made with WORDPRESS… simple… but complicated @ the same time.

anyway.. there are no index pages or categories or tags, no nothing!!

just one thing!
that once you enter the site, the following has to show up:

either:
1) a REGISTER form for user who havent registered…

OR

2) if they registered, then the same FORM has to show up but with the user’s data so that they can modify it.

nothing else.. THAT’s IT!

i dont know if this can be done with a special plugin or simply modifying the data that your tipical user can add if he wants to register.. like adding more fields or seleccion fields…

anyway..the form:
this is the complicated part i think, becuase it is divided into 3 different sections. you can’t go to section 2 without previously completing section 1.. and you cant go to section 3 without completing section 1 AND 2…

the form has its tipical fields like NAME, LAST NAME, EMAIL, and a few selection fields like YES or NO…

but also, the last component to the form has to allow the user to upload to his account anywhere from 1, 2, 3, or MORE photos to his account.

sorry for the long post, but ive been searching everywhere for a solution or a plugin and there is no simple way to solve this, at least not one that i can find. im at the office now still searching. so any help is appretiated.

the form obviously has to be then designed with CSS.. like field border colors and etc… but i doubt that will be a big problem.

i really dont know if im making this more complicated than it really is…

anyway. thanks a lot for your time, and i hope to find a solution to this as soon as posible.

thanks people ??