Have you tried looking in BOL (books online) under "Subscriptions [SQL Server query notifications]"?
You might also try out the entries from this results link. I went to http://www.msdn.com and searched on "SQL notifications subscriptions ".
http://www.bing.com/search?q=sql+notifications+subscriptions&form=STOHSS
However, it appears that notification services are on their way out in 2008, being replaced by functionality from reporting services.
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