Originally created and last_mod by whom and when ?

Hello,

In a web app (Pg 8.2.4 + php) I have product and other tables with fields like

product_created timestamp without time zone
product_created_user_id integer
product_last_mod timestamp without time zone
product_last_mod_user_id integer

The person who last modified an item can obviously be someone else who 
originally created it.

I can get the names and timestamps with two separate queries but how can I do 
a single query to get the names of both ?

product_id | 1
...
product_created_user_id | 1
product_last_mod_user_id | 2

ID 1, created by X / date and time, last_mod by Y / date and time

And a similar query to only one table, users ?

user_id integer
user_forename text
...
user_created timestamp without time zone
user_created_user_id integer
user_last_mod timestamp without time zone
user_last_mod_user_id integer

ID 4, name Z, created by X / date and time, last_mod by Y / date and time

Join, sub select ? I tried some but only managed to get only one name, errors, 
nothing at all or two rows with inner join + union ...

Lotsa thanks for any help,

Aarni
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