Wordpress's 5-minute install is still as lovely as ever (though most of the 5 minutes is uploading the burgeoning number of Wordpress files.) All you need is your Mysql username and password and it does it all for you.
I took a copy of this blog with LJarchive - another lovely easy to use piece of software. It saves your blog into a compressed .lja file: you can then export the whole thing, or yearly or monthly archives into XML files. It's a nice touch that it allows you to break up the file size, as Wordpress can only import files up to 20MB in size.
It took me a minute or two to work out where the import function was tucked away: the wordpress help says the file is in /wp-admin/import/livejournal.php, and indeed it is, but you can't run it from there, you need the Import link in the Tools menu. Then use the handy form to load in your journal and comments, and presto! A blog is copied. You lose your LJcuts and comment threading, but on the whole it's a fairly smooth process.
I wasn't able to find anything that offers completely effortless duplicate posting to both LJ and Wordpress, though the PressThis Bookmarklet comes close, you do still have to copy and paste. It would be nice if comments could be posted to Wordpress by email, that way you could use comment notification in LJ. If I cared enough about it I suppose I could try and write a plugin to do this, but at that point my curiousity was exhausted.