Over on his blog, my friend Michael Clark comes up with a function for turning Excel column letters into their ordinal numbers, (i.e. A = 1, B=2...ZZ=702). I've simplified the function here:
private int ColumnLetter2Number(string aLetterString)
{
const int ASCII_OFFSET = 64;
const int NUM_OF_LETTERS = 26;
char[] sourceArray =
aLetterString.ToUpper().ToCharArray();
return (sourceArray.Length < 2) ?
(int)sourceArray[0] - ASCII_OFFSET :
NUM_OF_LETTERS * (sourceArray[0] - ASCII_OFFSET) +
(sourceArray[1] - ASCII_OFFSET);
}