The following query returns all the clients who visited in 2008 and the year that the client previously visited or NULL if their first visit was in 2008). If I understand your requirements correctly, you should be able to categorise your clients based on the results of this query.

SELECT V1.Name, PreviousYear = MAX(V2.Year)

FROM Visit V1

LEFT OUTER JOIN Visit V2 ON (V1.Name = V2.Name AND V2.Year < 2008)

WHERE (V1.Year = 2008)

GROUP BY V1.Name

ORDER BY V1.Name