USE pubs
IF EXISTS (SELECT name FROM sysobjects
WHERE name = 'reminder' AND type = 'TR')
DROP TRIGGER reminder
GO
CREATE TRIGGER reminder
ON titles
FOR INSERT, UPDATE, DELETE
AS
EXEC master..xp_sendmail 'MaryM',
'Don''t forget to print a report for the distributors.'
GO
Above is the example from BOL. It creates trigger on table 'titles' for changes in 'pubs' database and calls stored procedure in 'master' database. What you need is to use the fully qualified name.