I have just made a release for my Java-based LJ client aimed at archival in XML. I still need to implement delete and edit capabilities, but as of now it is quite functional. It archives posts by month, so you'll have folders of different years, and Month.xml files in each. I.E. 2003/October.xml. Soon I'll add functionality for making posts friends only/private. LJArchive uses ranges for archival, so you can archive all posts, or specific ones by EventID (like "1-9, 42, 60-90")
Since it's Java, I'm quite sure it's multi-platform. I've tested it on many Windows platforms as well as Slackware Linux running at home. There are still bugs, I'm sure.
Please help test this! Eventually (using SWT) I'd like to build a GUI and make it pretty. For right now it's text-based.
If you're interested: Click here. For a feature list, visit my journal here.