Funny story about SQL Server 2005 on Vista

I just wanna be here to log a funny and annoying issue happened to me today.
I got to add a new login to SQL Server 2005 default instance.
And I got

User does not have permission to perform this action. (Microsoft SQL Server, Error: 15247)
Well, check out the permission of my Windows Authentication credential, it does have no sysadmin permission, but I cannot add myself to sysadmin because I'm told the same message: "User does not have permission to perform this action.", sounds pretty make sense...
So, I was going to login with 'sa'...
It told me 'Login failed for user 'sa'. Not associated with trusted SQL Server Connection'...
Attempt to enable 'sa' login:
Alter login sa enable
GO
It told me Cannot alter the login ’sa’, because it does not exist or you do not have permission. Follow the direction: "adding any user to systemadmin role"
-- I must go back to the previous error 15247.
Then, I try to reset [sa]'s password also with the commands:
ALTER LOGIN sa WITH PASSWORD = '<enterStrongPasswordHere>' ;
GO
And... try to enable mixed mode authentication.
-- NO WAY!!!
But this time it's a new nice friend of mine: 
The EXECUTE permission was denied on the object 'xp_instance_regwrite', database 'mssqlsystemresource', schema 'sys'. (Microsoft SQL Server, Error 229) 
... ... deadly desperate...
However, after some thinking of Vista's most famous sin: UAC, I try launching SQL Server Management Studio 'Run as Admin', and...
That's IT!!!
I was such a dum-dum...hope you will be no more :)

Have a NICE day!