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 www.msdn.com and searched on "SQL notifications subscriptions ".
However, it appears that notification services are on their way out in 2008, being replaced by functionality from reporting services.
Against stupidity the gods themselves contend in vain. -- Friedrich Schiller
Stop, children, what's that sound? Everybody look what's going down. -- Stephen Stills