Form validator problem. built in controls do not satisfy validation requirement.

[Girish]

I have 5 form fields on a webpage that I need to validate to check if they
are empty.
Heres the catch.

The form fields are divided into two groups. 2 in one group and 3 in the
other. Now the required field validation should only be on a group as a
whole.. sort of like a required group validation. To add another twist - if
one group has passed validation - the other group need not be populated.

This is my form:

US Applicants
---------------
Edu Level :
Zip Code :

International Applicants
------------------------
Edu Level:
City:
Country:

So either US Applicants group or International Applicants group should have
all their fields populated.

Is there a way to do this using a server side control? Im new to asp.net -
but it seems to me that even using the Custom field validator, its not
possible to use this cause in the custom field validator control you have to
specify the field you need to validate - and here there are 5 fields in
total.

Thanks in advance for your replies!
Girish