Hi Graham,
the server does not let you check in because you did not tell it your password, and Tortoise did not prompt you to tell it your password because you already communicated with the repository without specifying a password.
I don't know how to tell tortoise that it should use a password; frankly, I think this is kind of a bug of Tortoise.
But you could try to use SVN from the command line and check your code in via

svn import whatYouwouldLiketoImport --username jared --password shipit svn://opteron1/targetfolder

Right now I don't have access to a computer that is both online and has Tortoise installed, so I can't try to figure out how to do this more directly.