Reference URL: http://ccm.net/faq/8228-how-to-recover-windows-xp-admin-password

Steps:

Recover Windows XP Administrative Password
The first step in recovering your Windows XP password is to reboot your computer in safe mode. You can do this by restarting your computer and repeatedly pressing F8 as the computer loads. Once in safe mode, click on Start > Run. In the box that opens, type:
control userpasswords2
You will now have access to all user accounts, including that of the administrator. To reset the admin password, click on the Admin user account, followed by Reset Password. Enter a new password into the New password field and then confirm it. Save your new password by clicking OK.

Alternative

Taken from: http://ccm.net/forum/affich-57873-no-xp-pro-disc-and-lost-admin-password#q=how+to+retrieve+windows+xp+password+administrator&cur=4&url=%2F

Steps:

This method just worked completely for me, I am now operating windows in normal mode and happy to of impressed myself, lol! I decided to post this method in PLAIN ENGLISH, for those of us less computer savvy.

1. when windows is starting up press F8 (I had to attempt this a few times till I got it right, when I continuously hit the F8 key as fast as I could it worked, but you must begin hitting it as soon as windows begins to load)

2. (This will take you into a screen where windows lists different settings you can choose, as to how you want windows to run. I used the arrow keys on my keyboard, and selected safe mode)
select SAFE MODE

3. (for user name, type the word) administrator

4. (no password should be needed, so then press) enter

5.(windows should then load in safe mode. access the control panel by doing the following);
click start , control panel , user accounts

6. once in user accounts, find the name of the account that you need the password for, and
click on that account ,
then click on the option to remove the password for that account
THAT ACCOUNT IS NOW PASSWORD FREE !!!!

7. restart windows in normal mode and log in!

I also then managed to create (recreate) a password for that account as well, and then I created a guest account too!