Excel 2007 : Help with countif formula

Can anyone help me with the correct formula I would need to enter to count non duplicate cells in column a (cells range from a2 to a251) if b2 to b251 equals "jeff".

I have read in other forums that I can use the advanced filter option to create a copy of cells with the duplicate cells ommitted and then count them but I have quite a few names to sort by and would like excel to just spit out a number for me so i can enter it into a monthly bar graph already created.

Thanks in advance for all your help.