Alexander, the Robert Vieira SQL Server 2005 book does not mention the Snapshot Isolation Level, which is why I've stated there are only four levels in SQL Server 2005. You are correct however, the SNAPSHOT isolation levels were added in SQL Server 2005. This is an error on my part. The point still stands that you should be aware of the SNAPSHOT isolation level for the exams.
But BOL states that 2005 offers the four SQL-92 isolation levels, and additionally the SNAPSHOT isolation levels. Surprising that you tout BOL as the gold standard, yet you referenced a book. 😉
Is there any chance you can correct the article itself instead of simply acknowledging the error here?
Thanks,
Phil