Default timezones and Postgres

I am wondering how to force Postgres to simply store all time
information in the database in the UTC timezone. Is there a way to do
this that doesn't involve changing the timezone config of this entire
computer? What will happen is that we have users all over the world
in many different time zones. Each user will be able to set his own
prefs so that data will be displayed in his timezone. In this case,
the only timezone that makes any sense for internal usage is UTC,
right? Right now it seems to be storing everything in my local
timezone which isn't good.

Thanks for any sugestions.