To change the SQL sa password from a command prompt:
Start a command prompt by typing Start – Run – cmd
Enter the following commands, pressing Enter after each line
OSQL -S yourservername -E
1> EXEC sp_password NULL, ‘yourpassword’, ‘sa’
2> GO
Where yourservername is the name of your server and yourpassword is the new sa account password. Type exit twice to return to the server desktop.
This works in SQL 2005, I don’t have access to other versions so I can’t say if it will or won’t work other versions of SQL.