Year on Year YTD and YTD Flag Calculation at script level

[#1]

Dear Team,

I have a requirement to calculate the YOY YTD and YTD Flag.Please see the below excel.My requirement is

1) If I select July 2011 then my Year on Year Flag should able to pick the Jan 2011 to May 2011,Jan 2010 To May 2010,Jan 2009 to May 2009 and Jan 2008 to May 2008. It should exclude the 2 months from the current month.(In example i assumed July 2011 as current).Please help me in creating the flag for the same.

2) YTD Flag: It should show the all the Months by excluding the 2 months of the current month.in this case Jan 2011 to May 2001

2011	Volume	2010	Volume	2009	Volume	2008	Volume
Jan	5 MM	Jan	7 MM	Jan	1 MM	Jan	3 MM	YOY YTD
Feb	6 MM	Feb	8 MM	Feb	2 MM	Feb	4 MM
Mar	7 MM	Mar	9 MM	Mar	3 MM	Mar	5 MM
Apr	8 MM	Apr	10 MM	Apr	4 MM	Apr	6 MM
May	9 MM	May	11 MM	May	5 MM	May	7 MM
June	10 MM	June	12 MM	June	6 MM	June	8 MM
July	11 MM	July	13 MM	July	7 MM	July	9 MM
Aug	12 MM	Aug	14 MM	Aug	8 MM	Aug	10 MM
Sep	13 MM	Sep	15 MM	Sep	9 MM	Sep	11 MM
Oct	14 MM	Oct	16 MM	Oct	10 MM	Oct	12 MM
Nov	15 MM	Nov	17 MM	Nov	11 MM	Nov	13 MM
Dec	16 MM	Dec	18 MM	Dec	12 MM	Dec	14 MM

Please some one can help in generating these 2 flags.

Ram