--Also, here's a script for you while I'm at it. 

DECLARE

 @int_counter INT,

 @int_max INT,

 @txt_name NVARCHAR(255),

 @txt_sql NVARCHAR(2500)

DECLARE @databases TABLE (

 int_id INT IDENTITY(1,1) PRIMARY KEY,

 txt_name NVARCHAR(255))

INSERT @databases(txt_name)

 SELECT name FROM master..sysdatabases WHERE name NOT IN ('master','model','tempdb')

SELECT

 @int_counter = (SELECT MIN(int_id) FROM @databases),

 @int_max = (SELECT MAX(int_id) FROM @databases)

WHILE @int_counter <= @int_max

BEGIN

SELECT @txt_name = (SELECT txt_name FROM @databases WHERE int_id = @int_counter)

SELECT @txt_sql = '

 USE ' + @txt_name + '

 sp_changedbowner ''sa'''

--PRINT @txt_sql

EXEC sp_executesql @txt_sql

SELECT @int_counter = @int_counter + 1

END

--You might want to consider modifying to use sp_MSforeachdb.