I`m trying to install Ubuntu Server 9.10 on Vmware Workstation 126.96.36.199 but the installation stucks right here:
So how do I use the interface?
If you went through the setup, you can now login there with the user account you created during setup.
Ubuntu server by itself does not include a graphical interface (X Windows et al), as that edition is for servers. If you were looking for Ubuntu desktop (with a GUI) you can grab it here. If you don't wish to download another ISO you can use apt to install X and GNOME (the default that comes with Ubuntu desktop):
sudo apt-get install x-window-system-core xserver-xorg gnome-desktop-environment
you'll need to enable the Universe repository first then run
sudo apt-get update.