I use jbackup.pl to backup my LJ. It grabs posts and comments alike. I'm not sure it'll work with communities, but I'll test it out when I get home tonight if anyone wants.
Apropos of nothing, the hardest part of archiving SD is backup up the images. I wrote a program that went through the LJarchive backups to snag whatever scans were left online shortly after after SD 1.0 died, and the pics from that were several gigabytes, more than I could easily share without burning and mailing DVD's to people.