Import posts and comments
From b2evolution manual
This manual page is outdated. NEW PAGE: Import Posts and Comments in b2evolution v5+.
 Importing Posts and Comments
b2evolution has some built in importing features which you can use or modify to help import your blog from another blogging system.
 Importing from Movable Type
- Use MT's export functionality to create a .TXT file containing all your posts and comments. The important part here is to get your entire blog into one file. You usually do this by either setting your old blog to display a huge number of posts (more posts than you actually have) or to display a huge date range (which goes back farther than your first post).
- Place that .TXT file into the /admin folder on your server;
- In the backoffice of your b2evo blog, find the Tools tab and click on the link for the MT migration utility.
 Importing from LiveJournal
personman modified the built-in importer to work with LiveJournal blogs. Get all that you need from his site:
 Importing from Blogger
See this forum thread for instructions on how to migrate from Blogger.
 Importing from another blog engine
The general idea is to export all the posts and comments from your old blog into a .txt or XML file and then modify that file to work with the Movable Type migration utility. The above forum post may help with some of the modifications that are needed.
Another trick you can try is if your blog system has a way to export into Movable Type format then you can use that file with the MT migration utility.