Dreamweaver is definitely not the answer. I'm not sure microsoft visio is intended for web design style things?

Oh now i get it!

I wasn't to sure what you meant by structure? Do you mean physically structure (design wise) or the data flow structure / coding structure? By the looks of it, you have posted this in the wrong forum. May I suggest you repost in one of the coding based forums on this page http://www.daniweb.com/forums/forum31.htm

I was more refering towards the interface design with photoshop. I see what you mean now though.

After a quick google:

Try this link: http://www.osalt.com/visio and http://dia-installer.de/index_en.html

Let us know how you get on.