How to make a post to wordpress using the api?

yeah you can use metaWeblog.newPost or blogger.newPost, an example of the first:

http://www.wprecipes.com/post-on-your-wordpress-blog-using-php

uses curl and xmlrpc_encode_request

an example of the second:

http://www.nickycakes.com/post-to-wordpress-remotely-with-xmlrpc-in-php/

yeah and @Francis is correct