If you don't know the password, you can just use psexec to execute a command prompt as the NT SYSTEM AUTHORITY user. Then you can run oSQL commands, or open up SSMS which will let you create an SA user equivalent. This comes up from time to time, especially if you inherit servers.
1-Download PSExec from Microsoft.
2-use oSQL or find path to your SSMS (right click on the shortcut, get path or look for ssms.exe. Default path is:
C:\Program Files (x86)\Microsoft SQL Server\90\Tools\Binn\VSShell\Common7\IDE\Ssms.exe (I think 90 is sql 2005. Not sure, put in your path). I find oSQL easier.
3-Execute PSExec with a command shell with elevated admin privileges and open up SSMS or OSQL from psexec. If you want to open up a new window open up powershell.exe or cmd from
"C:\WINDOWS\system32\WindowsPowerShell\v1.0\powershell.exe" using psexec. For example:
psexec -i -c "C:\WINDOWS\system32\WindowsPowerShell\v1.0\powershell.exe"
Then create a new user and add it as an SA equivalent with something like:
CREATE LOGIN [NotSA] WITH PASSWORD=N'VeryStrongPW!' DEFAULT_DATABASE=[master], CHECK_EXPIRATION=ON, CHECK_POLICY=ON
ALTER SERVER ROLE [sysadmin] ADD MEMBER [NotSA]