Having long been an advocate of several open source content management systems, I’ve also done the difficult task several times of moving content from one system to another. Given these systems rarely (if ever) have built in export and import abilities (WordPress being one of them however), you can expect to do much of such a conversion by hand, one article at a time. If you have a large amount of content, obviously, this is a very time consuming and expensive endeavor. Moving users and passwords would require several complex database queries and testing as one must also understand how the passwords are encrypted. It’s a painful process and often too expensive for many clients to consider doing.
Here’s a resource to make this no longer an issue. CMS2CMS.com can make the conversion from one CMS to another in a matter of minutes. They’ve written the complex scripts needed to perform these tasks and appear to be adding to the list of what they can support all the time. They even have a script that will spider a site and push the content into the CMS of your choosing — take a look at the HTML to CMS path. Here is the full list of supported platforms.
I used their services to move a Joomla based website running on 1.x Joomla to the latest WordPress version and their tools captured all of the content and most importantly, moved all 138 members of the old site to the new. This was done in about 10 minutes time, including the time for me to put their “bridge” script on the client’s server. This allowed me to get the conversion done in an amazingly fast way — my client could not be happier. Me, too.