Registration
In order to download any of the Slater-Koster files, you should sign a license agreement, and fax it to the contact address therein. An account will be then created on this web page, which gives you access to the published sets.
Please note, that the account created for downloading the Slater-Koster files on dftb.org is independent from the one, you eventually obtained for downloading any DFTB implementations.
Follow this link to read and fill out the licence agreement for the download of the Slater-Koster files.