Suppose I installed a FixPack6's JDBC driver and constructed a
datasource to use this driver.  I then load the app server's classpath
with FixPack7's JDBC driver.  When I connect to a connection from this
datasource, which version of the driver is used by my code?

Thanks in advance,

When you connect to the datasource, java will attempt to find a registered
driver (loaded from the classpath) that can connect to the url.  So, for
your case, it'll be the Fixpak 7's JDBC driver.
However, be very careful not to mismatch JDBC driver levels with your
runtime client level. If you're using Fixpak 7 then you need to use the
Fixpak 7's JDBC driver.  Changing the classpath to point to another JDBC
driver can lead to unpredictable results.

-Michael