Seb7 - 4:01 pm on Sep 15, 2009 (gmt 0)

Personally, keep building the new site, and keep the old website up. Dont rush in to loosing the old site.

Start adding some links from the pages in the old website to the new updated pages in the website.

Once the new website gets good PR, and you see traffic over take your old website, then put the redirects in place. Which could be in a year or two.

Your old domain name is probably what has helped you get lots of traffic, and it would likely to have lots of back links. You dont want loose all that PR in your old website.