I’m currently in the process of redirecting traffic from an old blog (which is self hosted using Blogger) to a WordPress blog (which is also self-hosted.)
Since the old site is on an ASP server (Yuck! I know!) I didn’t have the luxury of using an .htaccess file, but I had to do it old school way, meaning meta tag redirect for the top traffic generating pages.
This is an example of a meta refresh tag here.
Use the 80/20 rule.
This would be a good time to target the top 20% of pages that generate traffic over the past year. Concentrate on those first, so that you would lose the traffic and worry about the rest gradually like those pages that get less than 100 visits or 10 visits per year according to your scale.
Another tip I recommend is if you don’t have your permalinks in place yet, that you do so as soon as possible. If your not sure of the permalink structure, you can always go ahead and use the post number, e.g. http://www.myblog.com/?p=150, that way no matter what structure you come up with, users will always be directed to the right post.