On occasion, I need to convert Excel files to CSV for parsing by other programs. A little Googling turned up a script from Jason Garber posted here. I'm including it here because it's (1) short, and (2) I had to tweak it a tiny bit for Excel 2008:

  # Convert Excel files to CSV.
  # Original from http://jasongarber.com/articles/2007/06/23/convert-excel-to-csv/
  # Minor modification for Excel 2008 dictionary to use "CSV file format" instead
  # of "CSV" in the save command.

  set theFolder to choose folder with prompt "Choose the folder that contains your Excel files"
  tell application "Finder" to set theFiles to (files of theFolder)
  set fileCount to count theFiles
  repeat with i from 1 to fileCount
      set fName to text 1 thru -5 of ((name of item i of theFiles) as text)
      if ((name of item i of theFiles) as text) ends with ".xls" then
          set tName to (theFolder as text) & fName & ".csv"
          tell application "Microsoft Excel"
              activate
              open (item i of theFiles) as text
              save fName in tName as CSV file format
              close active workbook without saving
          end tell
      end if
  end repeat

Thanks, Jason!