Blogging on Wordpress – Free blog now -> Move later to other host and it’s own domain?

I want to transfer a blog from another journal to wordpress.

I want to develop and create the design,layout/format of my blog before I move it to it’s own domain later on.

Can I do this? can I register a free blog on WordPress.. have everything published (content) and create the layout/design of the blog itself.. and then say, in a week or two, move everything to a .com (Dreamhost) ??? without losing my content and everything. I just want to prepare it before it goes “live” so to speak

*Or, do you have to register a blog made specifically for a domain and to be hosted elsewhere, seperaetly from the free wordpress blogs?

Blogging on Wordpress – Free blog now -> Move later to other host and it’s own domain?