I have a used macbook pro and I don't have the

You need to have the administrator password to manage administrators

This looks like you are using a Microsoft Windows Server computer or operating system. The "SAM" file is your password registry file for all the users within your domain controller (also why it asks you for your Active Directory users file). If you are expecting this to be something on your Mac, you may want to double check what you are trying to do. You might be installing Windows Server over your Mac operating system, or you may be installing a Server edition (instead of a personal edition) into a virtual machine.

Your best option is to use a Mac OS X install disk. Insert the disk, hold the 'C' key to startup from the CD drive, and there should be an option to reset your Administrator password. The details will depend on the version of OS X.

You can reset your password with the OS disc. Reboot using the disc and choose Reset Password from the menu bar.

Resetting a user's password
Note: These steps are for Mac OS X v10.3 or later. For information about resetting a password in Mac OS X v10.2.8 or earlier, see the Additional Information section below.

1. Log in with an administrator account. Tip: If you don't know the password of any administrator accounts, see "Resetting the original administrator account password" below.
2. From the Apple menu choose System Preferences.
3. From the View menu choose Accounts.
4. Click the lock button if it appears locked; enter the administrator password.
5. Select the username whose password you want to change.
6. Click the Reset Password button (Mac OS X v10.3 and v10.4) or the Change Password button (Mac OS X v10.5 or later).
7. Enter a new password in both the Password and Verify fields, and add a hint if desired.
8. Click the Reset Password button (Mac OS X v10.3 and v10.4) or the Change Password button (Mac OS X v10.5 or later).
9. If a dialog box appears with the message "Your Keychain password will be changed to your new account password," click OK.

If you have forgotten your password, if you have another user account with
administrative privileges you can log into that account and change your
original user account's password from the User Accounts applet in Control
Panel. If you don't have another account like this set up or don't have the
password to it, you'll need to log into the built-in Administrator account.
In XP Home, boot the computer into Safe Mode. Do this by repeatedly tapping
the F8 key as the computer is starting up. This will get you to the right
menu. Navigate using your Up arrow key; the mouse will not work here. Once
in Safe Mode, you will see the normally hidden Administrator account. The
default password is a blank.

In XP Pro, you do not need to go into Safe Mode. At the Welcome Screen, do
Ctrl-Alt-Del twice to get the classic Windows logon box. Type in
"Administrator" and whatever password you assigned when you set up Windows.

To change the built-in Administrator account in XP Pro if you can log into
another account with administrative privileges reset the password in the
Local Users and Groups snap-in in Microsoft Management Console (MMC):

1. Click Start, and then click Run.
2. In the Open box, type "mmc" (without the quotation marks), and then click
OK to start MMC.
3. Start the Local Users and Groups snap-in.
4. Under Console Root, expand "Local Users and Groups", and then click
Users.
5. In the right pane, right-click Administrator, and then click Set
Password.
6. Click Proceed in the message box that appears.
7. Type and confirm the new password in the appropriate boxes, and then
click OK.

If you reset the built-in Administrator account's password in Home or have
Pro and don't remember the password, use NTpasswd to change the built-in
Administrator account's password to a blank.

There's a "Change Password" utility on the install disk that the computer came with. If you don't have the install disk, there's another way, but it's a bit tricky...
Boot into single-user mode by pressing Command-S when the computer boots up Type the following: fsck -fy mount -uw / launchctl load /System/Library/LaunchDaemons/com.apple.DirectoryServices.plist dscl . -passwd /Users/{username} {password} reboot
make sure you replace {username} with the targeted user and {password} with the desired password.

You have to have your original administrator password for this. To change the administrator,

1. Open the Settings application.
2. Click the icon that says Accounts.
3. Make sure the icon that looks like a padlock (bottom left) is in the unlock position, if it is not: Click it and enter the Administrator username and password.
4. Go to the user you want to make administrator, and check the box that says Allow User to Administer This Computer
5. If you want to remove the previous administrator, you go to his user and uncheck that box.
6. Click the padlock to save.
7. Done!

Use F8 when booting to enter the boot options. Select safe mode
Log on as administrator, and click "yes" to the prompt that appears.
Go to the users control panel, from there you can reset your password.