Summarize:

Ubuntu is recommended by experts.  A “live” version allows you to boot into Linux without installing it. Put the disk into your CD Rom drive and restart the computer. When prompted to “press any key to boot from CD,” press any key. Depending on the version of Linux you’re using, you may be prompted to choose a version to use. Choose “Live” or “Try Linux” to access the Linux desktop. This will open the location bar. Make sure you type all 3 slashes (/). A list of hard drives will appear. Right-click on the hard drive that contains your Windows installation and select “Mount.” If there’s only one hard drive in the machine, it will be the drive that doesn’t say “System Reserved.” Now look at the top of the screen where you previously typed computer:///. Write down (or copy) the full path that now appears in that window. You’ll need it in a minute. You’ll be entering a series of commands into this terminal window, and they are all case sensitive. Type cd /path/to/windows/drive where “/path/to/windows/drive” is the full path that you previously wrote down or copied. Press ↵ Enter to continue. Do not type a slash, "/", in front of the word Windows. The directory names and path is case sensitive here. Type in sudo apt-get install chntpw and press ↵ Enter to install. Once you are returned to the command prompt, type sudo chntpw –u username SAM. Replace the word “username” with the account name of the Windows user whose password you want to erase, and remember that everything is case-sensitive. Press ↵ Enter to show a list of options. Press ↵ Enter, then y to confirm that you want to erase the password. Press the “power” icon at the top right of the screen to reboot the computer. Boot into Windows first removing the Linux CD. When the Windows login screen appears, you can now log in to the affected account without a password.
Boot the machine with a “live” version of Linux. Access the live Linux desktop. Press Ctrl+L. Type computer:/// and press ↵ Enter. Mount the Windows drive. Double-click the Windows drive. Press Ctrl+Alt+T to open the command prompt. Enter the Windows drive through the terminal. Type cd Windows/System32 and press ↵ Enter. Install and run the “chntpw” tool. Press 1 to clear the user’s password. Reboot into Windows.