Yes. Use the following settings within your blogging client:
Protocol/Provider: metaWeblogAPI
URL: http://www.squarespace.com/process/service/PostInterceptor
Your login name will be your website name (taken from http://<website-name>.squarespace.com/), and your password will be your owner account password. If your blogging client is also asking for a Blog ID, we recommend letting your client auto-detect all of these settings from the RSD file we publish.
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