Data Validation Query-formula building and making drop down button visible

hi there again. it seems like your last file only contains 3 months & now you got to adjust the formulas & your summary column to fit 4 months? doesnt seem like a good idea.

if you are ok with it though, this can solve your problem temporarily:
=SUM(OFFSET($A3,0,MATCH($O$1,$B$1:$M$1,0),1,MONTH($O$2)))

to show the dropdown button, you have to use form controls. can't remember where it is located in Excel 2003. got this from a website:

To add a combo box in Excel 2003 and in earlier versions of Excel, click the Combo Box button on the Forms toolbar.

http://support.microsoft.com/kb/291073

the pictures are showing Excel 2010 though. but after you get that form out, the processes are the same. do note that this is a separate object from the cell (unlike the validation in your file), hence you need to input a cell link & work with the formulas there. for eg, you can now directly link your formulas to O1. if u put the cell link in U1 for eg, it will reflect the choice number you select in the dropbox. i.e. if you select:
DRAFT PLAN -> U1 will show "1"
FIRST PLAN -> U1 will show "2"
FINAL PLAN -> U1 will show "3"