To change password of an user account, we need to go to User Accounts panel in Control Panel, choose the user account, click on ‘Change my password’ link, type current password once and new password twice. Too lengthy a process isn’t it? Here is handy tip to change Win XP passwords in DOS mode and believe me, it takes less than 5 seconds!! Let me share the hack with you all!
Steps to change password
- Click on ‘Start‘ and then on ‘Run…‘.
- Type ‘cmd‘ (opens up the command prompt).
- Now type net user
* (do not omit the spaces) - You will get a prompt like ..
Type a password for the user:
- Type the desired password and press Enter key. Also note that you wont see *****s as you type but don’t worry.
- You will again get a prompt like ..
Retype the password to confirm:
- Retype the password and press Enter key. Here too you wont see *****s as you type but don’t worry.
Thats it!!! Oh no .. wait .. Did it cost you more than 5 secs? OK Try this ..
Steps to change password quicker
Start all over again from Set #1 (above). In Step #3 above type net user username newpassword (do not omit the spaces) and press Enter key.
Switch profile and check your new password
This is another handy tip! Just press Windows key + L This will lock the computer and prompt you to enter password. Select the profile and enter the new password. If you get logged in that means the password is successfully changed. This again is another smart way to switch user accounts as also lock your computer.
Sounds good .. right? Try it. And hey .. you need to do this in administrative mode or else you will get an error messag: access denied 
[source]
Useful info. How to disable the turn off option when the system is locked?