Alex and I are currently testing the beta version of MetaWeblog API for MSN Spaces. So far we caught a couple of bugs and suggested a few improvements, but it looks like a good implementation. The main developer, Dare Obasanjo, is doing a great job and is very response to our emails. Thanks, Dare!
I don't know when blogging to Spaces with blog clients like ecto is available, but we will keep you up to date.