As of February 2008 1&1 has still only Debian Sarge (3.1) in their standard portfolio for initial installation. But the move to Debian Etch (4.0) is quite easy.
See the steps taken here
First you need to make a complete installation of the old Debian Sarge stable 3.1 system 64-bit via your 1&1 ControlCenter link.
After first login you can check your Kernel-Version with the following command: