The simplest way to do this is to have Fiddler capture an instance of this request and drag/drop that session onto the Request builder.
But generating a post yourself isn’t hard. Set the RequestBuilder’s method to POST, add a header:
Content-Type: application/x-www-form-urlencoded
And put in the Request Body the text of the post:
accountType=HOSTED_OR_GOOGLE&[email protected]&Passwd=yourpassword&service=finance&source=test-test-.01