Currently to access latest build artifacts you have to go in via the index.html in the latest folder. You cannot directly link to an artifact (eg you can type /download/latest/myArtifacts/myfile in the browser)
Chris wrote a patch to do this by analysing the file system (attached see method: checkForLatestDataPath)
This should probably be done by the URL re-write functionality.
[base URL]/download/[project key]-[plan key]/artifacts/latest/[artifact name]