Here is a couple of bits of code if you are using SQL Server:
Change wwf to your table prefix
CREATE TRIGGER Add_Welcome_PM ON [dbo].[wwfAuthor]
FOR INSERT
AS
declare @AuthorId int
select @AuthorID = Author_ID from inserted
execute wwfSpSendPM @AuthorID,1
CREATE PROCEDURE wwfSpSendPM
(
@AuthorID int,
@ForumID int
)
AS
declare @PM_Message varchar(200)
declare @PM_Subject varchar(50)
select @PM_Subject = 'This is a welcome Message'
select @PM_Message = 'Welcome to our forum, we trust you enjoy your stay'
select @ForumID = 1
insert into wwfPMMessage (Author_ID, From_ID, PM_Tittle, PM_Message, PM_Message_Date, Email_notify)
values (@AuthorID, @ForumID, @PM_Subject, @PM_Message, getdate(), 0)
GO