This should do it for you.... to use a conditional statement in a query use the iif() function. More information can be found in help.
SELECT tblHours.WorkerID, IIf(Sum([TotalHours])>8,8,Sum([TotalHours])) AS Normal, IIf(Sum([TotalHours])>8,Sum([TotalHours])-1,0) AS Overtime
FROM tblHours
GROUP...