=if(and(B8datevalue("10/1/07"),B8<datevalue("11/30/08"),0,if(and(B8datevalue("10/1/06"),B8<datvalue("11/30/07"),k8,if(and(b8datevalue("10/1/05"),b8<datevalue("11/30/06"),(n8+k8)/2,(k8+n8+q8)/3))))))

if between dates 10/1/07 - 11/30/08, calc 0
if between dates 10/1/06 - 11/30/07, calc total from cell k8
if between dates 10/01/05 - 11/30/06, calc value (n8+k8)/2
otherwise calc (k8+n8+q8)/3

Formula isnt working - any help would be great...Thanks in advance