Ben Hammersley has posted an index template to support RSD for Movable Type's XML-RPC implementation. RSD (Really Simple Discoverability) allows client software to auto-discover RPC services using nothing more than the URL for a blog. For example, this greatly simplifies the steps involved in setting up a desktop blogging client.
We'll be adding RSD support to the default templates in the next version of MT. You can use Ben's template (linked above) to support RSD now.