Group_concat equivalent in postgresql 8.2.11

The "not quite duplicate" in the comments should point you in the right direction: create your own aggregate function. First you'll need a non-aggregate string concatenation function, something like this:

create function concat(t1 text, t2 text) returns text as $$
begin
    return t1 || t2;
end;
$$ language plpgsql;

Then you can define your own aggregate version of that function:

create aggregate group_concat(
    sfunc    = concat,
    basetype = text,
    stype    = text,
    initcond = ''
);

Now you can group_concat all you want:

select group_concat(s)
from t
group by g

I dug this out of my archives but I think it should work in 8.2.

Keep in mind that 8.2 is no longer supported so you might want to upgrade to at least 8.4 as soon as possible.