How Do I create a running total of unique values?

[bonfire09]

I want something like this as shown below where I count the # of unique category values. I was  trying
count(distinct [category]) but it was not working.  Any help would be great thanks!
category count
a             1
a             0
b             1
b             0
a             0
c             1
c             0
c             0

[MFGF]

I want something like this as shown below where I count the # of unique category values. I was  trying
count(distinct [category]) but it was not working.  Any help would be great thanks!
category count
a             1
a             0
b             1
b             0
a             0
c             1
c             0
c             0

How about total(1 for [category])

MF.

[bonfire09]

Thanks! I tried this but it did not work. Instead I brought in another column and did a running count on that grouped by the category column. IE

running-count ( [data item] for [category]) which gave counts within category, and then created a new query calculation that had a case statement that said

case

     when running_count=1 then 1
else 0

end case.