Purpose
b₂evolution already has methods for importing blog posts from Wordpress, b2/cafelog and Movable Type. I've modified the Movable Type importer to create a LiveJournal importer.

Installation
Requires b2evolution 0.9.x or later

1. Download this file: import-lj.txt.
2. Remove the .txt from the filename and add a .php extension, then upload it to your b2evolution admin folder.

3. Edit the /admin/tools.php file and add this section:

   <div class="panelblock">
<h2><?php echo T_('LiveJournal Import') ?></h2>
<ol>
<li>Use LiveJournal's <a href="http://www.livejournal.com/support/faqbrowse.bml?faqid=8&q=export" title="LiveJournal documentation for exporting posts">export functionality</a> to create an XML file containing your posts.
<ul><li>Exports done in this way will not include comments.</li>
<li>LiveJournal's export page creates a separate file for each month, requiring you to run the importer multiple times</li>
<li>To get an one XML file with all of your posts and comments, use <a href="http://sourceforge.net/projects/ljarchive">ljArchive</a></li>
<li>This importer is compatible with either method</li>
</ul>
</li>
<li>Place the XML file in the /admin folder on your server</li>
<li>Follow the instructions in the <a href="import-lj.php">LiveJournal migration utility</a>.</li>
</ol>
</div>

Usage
Go to the Tools tab and you'll see the instructions that you added in step 2 above. Get your xml backup file from LiveJournal using ljArchive. LiveJournal has their own export page, but it only archives one month at a time and it doesn't include comments. ljArchive is the preferred method, but the importer will work with either method. Upload the xml file to the admin folder and run the importer. You'll be able to choose which author and category you want assigned to the LiveJournal posts.