I am trying to Sum a Year to date range based on a month reference. Ideas?

Sheet 1:

Jan05 Feb05 Mar05
12345 12 34 56
67890 78 90 12
23456 34 56 78

Sheet 2:
Column 1 Column2
12345 =SUMIF(CustNum,CustNum2,INDIRECT(Month))

Column3 (Not working)
=SUMIF(CustNum,CustNum2,INDIRECT(CONCATENATE(Month ,"Total")))