Hey all you EXCEL wizards! Can you please help?

I'm collecting performance metrics by month, each metric in a row. I'd like
to put a cell in the top of the page that would allow the user to pick the
month from a validation list that is tied to the column headings (month names
in row 5, columns J through U).

When the user defines what month it is by choosing from the list, I would
like a "year to date" column to add the correct number of columns for a YTD
total, i.e. if March were chosen, the sum of J, K, and L would be shown in
the YTD cell.

Any ideas? Thanks for the help.
--
Pat Rob