If u want to hack password of xp :-

method 1

(it is useful for school clg computers )
if u login with a limited account or guest account and want to crack administrator account
just goto run.
type lusrmgr.msc
choose user
in right side find administrator right click on it and choose set password .
set any password or leave it blank.

method 2

For real hackers

if u want a xp system and can't login with any account then
1.first make a administrator account in your system without password
2.Using a ntfs editing tool like ntfs pro copy your SAM file from your pc it is
located on c:\windows\system32\config & c:\windows\system32\repair .
3.the next step is to make a DOS bootable disk u can use NERO8 for it including your
SAM file and NTFS editing tool.
4. just go to the system u want to hack put this cd and boot from cd replace your SAM file with that computers.
♥thats all♥