You can install L0phtcrack from
www.atstake.com
but its a shareware.
Other good workarounds can be seen here
*www.experts-exchange.com/Operating_Systems/WinXP/Q_20348448.html
Or else you can try this method...
My computer -> right click -> manage
Computer Management (Local) -> System Tools -> Local Users and groups -> Users -> Administrator (right click) -> Set Password
give the new password.
If you have some encypted data, then it will be lost.
By the way... there was some discussion over this earlier too.
so search the forum you will find some other ways to tackle the problem too