Tuning, JDBC, Tomcat, RedHat: Help, please.

Hi,

I'm in a bit over my head, and I was wondering if you could help me. I've
searched the archives, to no avail, but perhaps I'm just not choosing the
right keywords.

I've been testing some code that someone else wrote. Jsps served by Tomcat,
using JDBC to talk to PostGreSQL. And I'm charged with not only testing it
(which I can do), but fixing it (which I fear I know little about).

When I have 20 concurrent users running huge queries through Jmeter,
PostGres bogs down horribly. PostGres and the Tomcat installation are both
running on the same box. (RedHat7.0, probably completely vanilla install --
still 2.2.16 kernel, living behind a firewall right now.) I believe the
PostGres version is 7.1.2 (although I'm not certain of that).

Can anyone tell me where to find out about:
a) tuning PostGres -- I've read the page about tuning kernel parameters, and
upping SHMMAX and SHMALL didn't seem to help my problem.
b) JDBC connection pooling
c) making tomcat throw a nice error page rather than "can't do that,
couldn't get a handle, here's a stack trace"

Thanks,
Sarah