I've just finished work on the beginnings of a new MySpace API for .Net. I'm writing it in C# and accomplishing most of the work via a state machine and web browser automation. The only thing it does right now is post new blog messages. I plan on using it to allow interBlog (from the interquire interWeb Web 2.0 suite) to sync a user's posts with their MySpace account.
If there's much interest in a full-blown API, I'll develop it further.
Download the interquire.MySpace.dll version 1.0 here
To use the API in your code:
Blog b = new Blog(txtEmail.Text, txtPassword.Text);
b.NewPost(txtSubject.Text, txtBlogText.Text);
if (b.error)
MessageBox.Show(b.errorText);