How to convert 3 colums to timestamp with timezone

Hi There!

Hope this is an easy one :-D

How do I convert 3 individuel colums with type "date", "time" and
"integer" to at timestamp with timexone?

eg.   tabel
cStartUnixtime    cStartTime    cStartZone
09-24-2004    10:27:12    -2

This I have to present as an timestamp with timezone.

Thanks in advance
Jens Arnfelt