Here's another way to change your root password on Linux, which avoids the having to tweak boot options when you use GRUB(a pain to do), instead using a LiveCD. If you have a second Linux system, you can use that instead, and it might even be possible to do it from Windows, but it would probably be much harder.:

1. Get a normal LiveCD. Knoppix will do, as will the Gentoo LiveCD. All that matters is that it boots into some sort of semi-normal Linux from which you can get a normal command prompt, and not some specialized program. If you have a second Linux system, skip this step and boot to it instead.(You'll need root on it though)

2. Mount your directory structure under some subdirectory of the LiveCD system. For the Gentoo LiveCD, there's a /mnt/gentoo designed for this purpose.(You can still use it even if you're not using Gentoo--it's called that because the LiveCD is for Gentoo installation) In Knoppix, apparently the drive will be mounted for you already. However, since I don't use Knoppix, I can't vouch for that.

3. chroot to this subdirectory. To do so, type in chroot (directory) or simply cd to the directory and type in chroot . and you're set. You'll have a root prompt.

4. Run passwd.

To run you through this without the extraneous comments:
1. Get a LiveCD, or boot to root on a second Linux system on the same computer.
2. Mount your Linux system in a subdirectory, if it's not done so already.
3. chroot to said directory.
4. Run passwd.

And that's it!