I know it's not necessarily answering the original question, but whilst helping someone else today, I discoverd the
sumproduct function which I'd not discovered before.
So just incase it helps anyone in the future, this site has quite a good overview of the capabilities of sumproduct :
Help using the Excel SUMPRODUCT() function
acbus1,
Re. your second question, perhaps an indirect reference might be along the lines of what you desire ?
Help using the Excel INDIRECT function