Running a query as a specific, different user

Hello all!

I'm working on a report (using jasperreports) for an application I've
written accessing PG 8.1.4.  The view I'm doing the report on needs
to run as a the specific user requesting the report; however, the
report is connecting to the database using a general username for the
report itself.

Is there a way within the SQL of the request to get a query to
execute as a specific user?  In effect changing the user in the
middle of a connection?

Thanks!
Mark