composite primary key to foreign key - Mailing list pgsql-novice

I have a table with 4 columns, 3 of which make up a composite primary key.
None of these columns are unique, but the combination of the the three
primary keys will be unique:

CREATE TABLE Table1 (
   col1 integer,
   col2 varchar(20),
   col3 varchar(20),
   col4 varchar(20),
   CONSTRAINT PRIMARY KEY (col1, col3, col4)
);

In another table I have 3 columns:

CREATE TABLE Table2 (
   field1 integer,
   field2 integer,
   field3 integer,
);

I'd like to have field2 in table2 be a foreign key of col1 in table1.  Since
col1 is not unique, is this possible or do I have to either bring in
extraneous data from table1...col1, col2, and col3, or create some unique
counter in table1 to use as reference?  All I care about in field2 of table2
is that it matches something in col1 in table1, I don't want the other data
in table1.  I've searched archives but maybe I'm not looking for the right
thing.  Thanks.

-Ryan