In the SQL Server 2008 Upgrade Technical Reference (KB + 490 page doc) there is a short chapter, Chapter 9, that addresses Notification Services. You may download the document from the link at the top of the KB page here:
http://msdn.microsoft.com/en-us/library/cc936623.aspx
Here are the first paragraphs of the chapter:
SQL Server 2008 does not include Notification Services; SQL Server 2005 is the last version of Notification Services. However, you can get the latest SQL Server 2005 Notification Services Components Package, which has been updated to allow Notification Services to work with a SQL Server 2005 or SQL Server 2008 database instance. The "Feature Changes" section that follows describes the Components Package in more detail.
SQL Server Notification Services provides a robust platform for developing and hosting notification applications. A Notification Services application lets subscribers select information that is important to them and then automatically receive notifications when an event occurs that matches their criteria.
Notification Services is based on SQL Server, XML, and the .NET Framework and offers a rapid development platform for creating notification applications. It has built-in capabilities to handle real-time and scheduled notifications; multiple languages and time zones; extensible event, content formatting, and delivery channel options; and flexible deployment scenarios.
This chapter describes the steps you need to take to use Notification Services in SQL Server 2008.
[the article continues with how-to information… please see the document, chapter 9, for full information]