trigger postgresql 7.4

Hi,
I have a question connected with postgres procedural langauge. Version
of Postgres:

"PostgreSQL 7.4.2 on i686-pc-linux-gnu, compiled by GCC gcc"

I have a table on which I have created many triggers on the same event
BEFORE UPDATE.

I have 3 these triggers. In each of this trigger I have a statement
RETURN NEW or ''RAISE EXCEPTION".

My question is:
1. In which order (first, second, third) each trigger is executed?
I think that triggers are executed in order by oid or by name. Tell me
please.

2. Is it possible that next trigger on the same event is not executed
when the previous one has returned "RETURN NEW"?

3. The last question is, is there any debbuger to debugg triggers in
plpgsql? This could be very usefull.

Please help,
Daniel