I can not boot in single user mode without root password

[rosetta]

hi

  I am using the kernel-2.6.11-1-386 and grub.
  In boot menu, I have choosed the "recovery mode". But while the
system boot completely, it prompt "Give root password for
mantenance(or Control-D to continue):".
  If I press ctrl+d, then it will use normal runlevel.
  How can I use 1 runlevel if I forget the root password in grub?

  best regards