This was fixed in previous grml releases (forgot to update this bugreport 
accordingly, sorry). Nowadays we've

#define COMMAND_LINE_SIZE 2048 

in linux-2.6/arch/x86/include/asm/setup.h.

Closing this bugreport therfor, if you still encounter any problems fill free 
to reopen, thanks.

regards,
-mika-

Since the syslinux/isolinux/pxelinux APPEND lines get rather long, it's easy to
run into the size limit of 256 chars, either by having the nfsroot in a
/very/very/deep/and/hidden/hierarchy (which could be avoided) or when trying to
pass a couple of additional parameters.