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’
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.