forget admin's password in xp
press F8 while booting, select safe mode with command line.
select administrator account to login (don't need password)
use "net user owner 123456 /add" to change owner's password to 123456
"net user abcdef 123456 /add" to add a user
"net localgroup administrators abcdef /add" to make abcdef an administrator
reboot, then abcdef has administrator's privilege.
now you can use abcdef as administrator to assign a new password for anyone.