Login to the server where the oracle database resides as user oracle(user who installed the oracle software and belongs to the dba group) and connect to the database (make sure you export ORACLE_SID to the required/target database) using sqlplus as "sys as sysdba". When prompted for password just press enter. This will login you to the database as sysuser. Then do "alter user sys identified by new_password;".
In windows the user should be a member of ORA_DBA group. Then connecting as sys as sysdba will not prompt for the password. Change password as show above.
Else you can always work use orapwd to create a new password file.
Amar "There is a difference between knowing the path and walking the path."