now() AT TIME ZONE interval '-5 hours' returns type interval???

I am attempting to work with time zones.  All of my timestamp fields are

timestamp with time zone

The problem I am having is when I attempt to convert a timestamp with a time
zone to another time zone.  For example, the statement

SELECT now() AT TIME ZONE interval '-5 hours'

returns type interval not timestamp with//out time zone.

On my website I have people select the timezone they are in..

That way I can theoritically perform an insert along the lines of

timestamp '2003-12-03 19:34' AT TIME ZONE interval '-5 hours'

replacing -5 with whatever timezone they specify.

I am hoping to be able to do the reverse,

SELECT stamp AT TIME ZONE interval '-5 hours' FROM table;

However it returns type interval!!!  And casting it to type timestamp does not
work.

Help!

Josh.