Date format issue

Hello All...

In my query of time zone i have details of interval with me like '-9:00',
'+5:30' etc

my problem is regarding the format of Date which i receive... ie. when I add
the interval field the results are like:
Query:
select current_date at TIME ZONE "interval" '+5:30';     timezone      11399908 years 8 mons 1538 days



but instead of  interval when i run query like"
Query:
select current_date at TIME ZONE 'IST'     timezone      2004-03-17 20:30:00


I want the format should be like 2004-03-17 20:30:00
How can I do that with INTERVAL information with me?? pls guide me..

Also can I have link to some doucmentation where i can read about Date/Time
zone related theroy/functions??

thanks in advance..

regards,
Raman Garg