IFF syslinux is not installed, grml2usb reacts not very helpful, see below.

$ grml2usb -v
grml2usb 0.9.25
$ grml2usb /download/grml-medium_2010.04.iso /dev/sdc1 
Executing grml2usb version 0.9.25
Using ISO /download/grml-medium_2010.04.iso
Identified grml flavour "grml-medium".
Copying files. This might take a while....
Installing default MBR
Installing syslinux as bootloader
Traceback (most recent call last):
  File "/usr/sbin/grml2usb", line 2079, in <module>
    main()
  File "/usr/sbin/grml2usb", line 2066, in main
    handle_bootloader(device)
  File "/usr/sbin/grml2usb", line 1999, in handle_bootloader
    install_bootloader(device)
  File "/usr/sbin/grml2usb", line 698, in install_bootloader
    install_syslinux(device)
  File "/usr/sbin/grml2usb", line 672, in install_syslinux
    proc = subprocess.Popen(["syslinux", "-d", "boot/syslinux", device])
  File "/usr/lib/python2.5/subprocess.py", line 594, in __init__
    errread, errwrite)
  File "/usr/lib/python2.5/subprocess.py", line 1153, in _execute_child
    raise child_exception
OSError: [Errno 2] No such file or directory