Does Hetzner support Windows Server 2008 ? How to install it?

We do not offer Win 2k8 since quite a while.
So you can only install Win 2k8 if you have your own license.
You can order a LARA (KVM) in your client webinterface (robot) directly at the server at the tab "Support"->"server requests"->"remote console (LARA)". This LARA has a virtual media support, with which you can mount and install an image.
http://wiki.hetzner.de/index.php/LARA/en#Installing_an_OS
We cannot guarantee that the virtual media support works in any case.
If it does not work you can send us a link to an ISO file, which we burn on DVD or copy on a USB stick.
You can then install the OS yourself by LARA, which our technicians will connect to your server after making an appointment, along with the DVD or USB stick, on which your ISO is available. The option for connecting and disconnecting of DVD drive or USB stick costs 21.01 € (excl. VAT) once.

Windows 2008 R2 .iso image (30 days trial): http://getintopc.com/softwares/operating-systems/windows-server-2008-r2-free-download/
How to rearm Windows trial: https://www.youtube.com/watch?v=1-Nqe27Epj8
Related topic, where to buy cheap Windows Dedicated servers: ​http://internetlifeforum.com/dedicated-server-hosting/3749-cheap-dedicated-servers-windows-server-license/