Format date/time according to time zone.

I have an asp page that displays information from an xml document. I use
an xslt doc to format xml data and produce the asp page. One bit of data
from the xml doc is the data/time stamp. The time stamp is in GMT. I
want to change the GMT to reflect the time zone I'm in. I want it to be
4 hours earlier. Is there method to format date/time in xslt?

Here the code I have in xslt doc to extract the date/time from the xml
doc.
<xsl:value-of select= "rpuData/essIdent/@TimeStamp" />...
it returns something like this 12/30/2004 18:05  the date is correct
but the time is GMT I want the time to be 12/30/2004 14:05. 
 
Thanks
K Doran