Hi Joanne,
We did the same thing recently for a client who wanted to move from a .com to a .co.uk. She had a well-established website. Our methodology:
- Create exactly the same URL structure and architecture.
- Copy the exact same content over to each URL
- Notify all websites linking to any pages to update (We actually did this part well in advance).
- Notified Google via its webmaster tools that we are migrating to a new website. You can use their new site section to notify them.
- 301 redirected every page of the old site to its new equivalent page.
The sit back and wait, we found the changeover within the SERPS fairly fast – there were a few hiccups while waiting for Google to fully update, however it worked and all PageRank now on site and older positions are almost all regained.
Hope that helps.