There’s an import script, available through the Tools in the Back-Office that lets you import your MovableType blog into b2evolution.

1. 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).
2. Install b2evolution the regular way
3. Once b2evolution is up an running, place the previously exported .TXT file into the /admin folder on your server;
4. In the backoffice of your b2evo blog, find the Import Tab and click on the link for the MT migration utility.