unique column value from dataset to dropdownlist

[gane kol]

Hi

I have a dataset with counties, city, state and zip.
for a zip, the dataset can have multiple cities, but with same state and
counties in the records.
I need to databind the county dropdownlist with the distinct county value
in the rows.

for eg:
my dataset looks like:
monroe | Piscataway | NJ | 08854
monroe | South town | NJ | 08854
monroe | RiverBend | NJ | 08854

so for the zip code 08854, i need to populate the county dropdown with
"monroe".

Any help or links appreciated.

Thanks
gane