can anyone explain me the difference between Dreamweaver and Dreamweaver ultradev?
TIA

Ultradev is for the development of Database Applications in your Web server (It offer all the Dreamweaver features plus this) so unless you are developing a big Commerce site with a back end database you do not need it.

the ultradev versions the same purpose?

http://www.macromedia.com/software/ultradev/productinfo/features/