Need to import data in a 1:N relationship

Hi

Is it possible to import data in an a 1 to many relationship. I have an entity X which is having relationship with opportunity. An opportunity an have X objects associated with it. The data of X and opportunity is already available in excel file and I can import data in both X and Opportunity. But don't know how we can import data such that when I am finished with import it must show X already associated with Opportunity.

Thanks in advance.