Magic, pretty much. At least, I don't *think* you need to change anything.

Since AutumnVet is Wordpress-based, it automatically publishes what we call an "RSS feed" of everything you post there -- basically, a computer-readable version of your postings. And LJ has a paid-user feature for turning RSS feeds into pseudo-accounts in LJ. (LJ calls them "Syndicated Accounts".) So I just have to plug the two pieces together, and it should start to work automatically in a day or two.

I'll try it this afternoon...