How to insert into another db instance in pl/plsql...

Hi,
    I this question seems out of place on the other mailing lists, so I
posted here.

    Basically, the problem is this:
I have 2 database instances. InstanceA & InstanceB
In InstanceA, I have a trigger on a table which, when activated, will
insert a row into some table in InstaceB.
The trigger is written in pl/pgsql.

How can this be done?

Any help would be greatly appreciated.
Rick