counting unique entries for a specific date period in a series of dates

Hi,

Hi, I am looking for a formula to count the number of unique entries within a specific date per month peroid.eg

01.05.09 log 1
05.05.09 log 2
20.05.09 log 1
05.06.09 log 1
06.06.09 log 3
07.08.09 log 1
09.08.09 log 1
10.08.09 log 1

may contains 2 x log 1 and 1 x log 2
june contains 1 x log 1 and 1 x log 2
aug contains 3 x log 3

formula would be how many log 1 entries are contained between 01.05.09 and 30.05.09 answer would be 2.

@countif(a1:a20,"log1", between 01.05.09 and 30.05.09)

So it searches through the series of dates and when when it come to between 01.05.09 and 30.05.09 if counts the number of "log1" entries. and gives a value of 2.

Hard to explain, but can anyone help .

The data is contained in 2 colums, i.e the date is in colum A:1 and the data is contained in B:1.

cheers