one of the way is using triggers. which will fire in the case of insert,update or delete on that table. in that trigger code, write an Email send code which will sent the email to the users.
to send email to the users from sql server,
http://forums.asp.net/t/981809.aspx
or you can use windows service which will runs automatically, in that windows service, write a stored procedure which will check the changes in records and sent the email to the users. here you can send email from the front end.