Use grml-x name_of_windowmanager to start X with your prefered windowmanager. For example:
grml-x wmi
will start up the Xserver using the windowmanager WMI. Other windowmanagers provided by the grml-system can be listed via pressing the tab-key after entering 'grml-x' in the commandline (using the zsh-completition).
grml-x fluxbox -- :8
will start another Xserver using the windowmanager fluxbox on tty8.
You might want to add a swapfile because you need more space in the ramdisk.
mount /mnt/hda1 # the partition you want to use as a swap file, adjust it!
dd if=/dev/zero of=/mnt/hda1/swapfile bs=1024 count=524288 # for a 512MiB swap file
mkswap /mnt/hda1/swapfile
swapon -a