timestamp wiht time zone

Hi,
i have a column in my table defined like this:

time_stamp timestamp DEFAULT ('now'::text)::timestamp with time zone

Data gets filled in this column from a Unix tools server.

Example values of this field are:

time_stamp
--------------------------------------------
2007-06-27 14:52:14.760133
2007-06-27 15:06:56.90582

I have the following questions on this field.

1. What is the value after the dot (period) at the end. Like 760133 and
90582
2. How does it talk about the time zone.

Also, the reason I'm using time zone is that I have to compare different
values in the tables correctly without any error(s)
based on time zones.

Any kind of help would be greatly appreciated.

Thanks,
~Jas