A client wants to \"Web-enable\" a spreadsheet calculation -- the user to specify the values of certain cells, then show them the resulting values in other cells.
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The simplest way to do this might be to:
Upload the Excel workbook to Google Docs -- this is very clean, in my experience
Use the Google Spreadsheets Data API to update the data and return the numbers.
Here's a link to get you started on this, if you want to go that direction:
http://code.google.com/apis/spreadsheets/overview.html