Migrating from other CMS to WP – losing SEO juice?

I’m thinking about migrating a client’s website from a super-old cms (xoops) to WP. However the site is quite old so I don’t want him to lose any SEO juice he acquired through the years (PR: 2). Anything I’d have to consider doing the migration? (I was thinking about setting up WP on a separate folder and then moving it to root for the full migration – anything I have to consider here?)

Thanks a lot!

Edit: Mike Hudson (comment below) made me aware of an error. I thought PR = Ranking in the results. Meaning: I’m more concerned with the ranking than the PR, so redirect is the way to go! Thanks folks!

You should use a sitemap module to generate a list of URLs created by XOOPs [e.g. xSitemap].

Then you have to set up your .htaccess to 301 redirect each URL to its corresponding page in the new WordPress instance.

Finally, you should consider installing a WordPress plugin like Redirection to check for 404s and redirect them nicely to the new instance.