Dara Roesner’s WordPress plugin for embedding Metaplace worlds is now up on WordPress.org. So you can grab it there, or you can go to your Dashboard, click Plugins, click Add New, and search for “metaplace.” There will be two results, actually, because SignpostMarv’s MetaverseID plugin also supports Metaplace. 🙂
In any case, from there you can install the plugin automatically! It supports both a sidebar widget and a tag for putting worlds within page or post content.
A few other embedding options have popped up already, by the way. There’s a phpBB setup walkthrough here as well, which will add [metaplace][/metaplace] bbCode to your forums. A few folks have also put it in an iGoogle gadget.