Excel 2000 – COUNTA function

I am looking for a variation of the Excel COUNTA function that will count NON-DUPLICATE entries in a range of cells. For instance, if the range contained entries of 1,4,x,y, the value would be 4. If, however, the range contained 1,4,4,x, the valuewould be 3 as it only counts the first entry for the number 4.

Data valadation or drop down lists are not a viable choice with this application as I do not know what all the possible entries could be. Any ideas? Thanks – Kevin.