(i'm writting this under the assumption that you don't know php/mysql)
first things first, .. you really need to get a basic understanding of php. personally, i like to thumb through a book when getting introduced to a language because there is usually a nice balance of information on the different aspects of the language.
if that is not your style, then there is a LOT of information on the internet in the form of tutorials and what not.
besides identifying where your resources are ( here,
http://php.net , google, etc .. ), the best way to learn is by just doing it. start with something simple. maybe you can find a good tutorial such as "hello world" in the articles section (
http://php.codenewbie.com )
the questions as you asked above are a little too much to answer in 1 post, but it is good to ask questions. there are a lot of people willing to help on forums, but just make sure you ask questions as specific as possible.
take your project in little chunks. focus on the drop down issue first. if your post is specific, people, like me, are more able to help you since there can be a somewhat brief answer. .. then keep asking about it, or move on to the next small item.
for learning PHP, it is important to learn and understand how to use mysql with it. it may be very intimidating at first, but it really is not a big deal after coding a few scripts. again, when you get to this point, post your questions on this very specific subject.
well not sure i can really be more help in this post, but good luck .. see you in the PHP forum.