Insert Windows CD then go to Recovery Console
TYPE net user
it will display list of user/s in ur PC this justlike this..
G:\Documents and Settings\lipu>net user
after this type net user user_name *.
here user_name is the user name of which you want to change the password. it will ask a new password and to confirm it. In my pc this is like this..
G:\Documents and Settings\lipu>net user administrator *
Type a password for the user: leave it blank and press enter
Retype the password to confirm: leave it blank and press enter
The command completed successfully.
ur password has been reset/disabled