We must know that Windows XP’ password stored in Windows \ System32 \ Config under the SAM file.Ok,the you may know how to do.
Step 1:Login to a Computer that has Windows XP system.
Step 2:Copy the SAM file to a floppy disk.
Step 3: Then turn to your locked pc and insert the floppy disk Reboot the PC and enter into MS-DOS.
Step 4:In dos,type : del c: windows\system32\config\sam ,then you will delete the SAM file.
Step 5: type : Copy a:\sam c:\ windows\system32\config,copy the other’s SAM file to your PC.
Or you can google Windows Password Key