Filter by Form & linked combos

Hi the

I have the following question:
I have a country table (countryid, country_name) with values as:
0, "Mexico"
1, "USA"
2, "Canada"
for example.

I have a city table (cityid, countryid, city_name) too, with values as:
0, 0, "Guadalajara, MX"
1, 0, "Zacatecas, MX"
2, 1, "L.A. US"
3, 1, "Denver, US"
4, 2, "Toronto, CA"
4, 2, "Ottawa, CA"

Then I linked this tables using the Relationships feature of access 2003.

I created a form with two fields, country_name and city_name.

The problem is: when I execute the form and enter to the "Filter by Form"
view I select "USA" in the country field... I expect to see only the cities
that belong to America in the city field but ALL the cities in the city table
are shown.

How can I filter the city field to show only the values releated with the
country field in the "Filter by Form" view?

Any ideas? What am I doing wrong?

Thnk for your help

TMM