ced1870 on "customize the admin screen of a plugin"

Hi
I'm new to wordpress and I'm playing with my new toy :)
I'm trying to create a plugin, it is ok for the first steps. Now I have menu entry with a specific post_type and when editing the items I would like to not have the standard layout.
Instead of "edit item, new" and the default fields , I would like to create my own PHP/HTML/CSS layout to give more control and options.
As I'm new I don't know how to do that, may be someone here can help me and give me few suggestions :)
Thank you !
CEd