here's some neat information to help
Problems Using The Proxy Server

I have Internet Explorer running on a Mac. Why can't I use the proxy
server?

No version of Internet Explorer for the Macintosh, including IE 5.0,
has the "Automatic Proxy Configuration" capability. It is not likely
that Microsoft will address this problem. We suggest you download
Netscape if you want to use the proxy server.

When I configure Netscape to use the proxy server on my Mac, the
machine crashes. What can I do?

Netscape 4.x crashes on the Macintosh (but only on the Macintosh) when
configured to use the proxy server. The cause for this seems to be an
unpublished limitation on the size of the proxy server automatic
configuration script in the Macintosh implementation of Netscape 4.x.
Evidently around July of 2001 the number of resources listed in our
automatic configuration script (from URL
http://proxy.lib.berkeley.edu/proxy.pac) caused the size of this file
to exceed this unforeseen limitation.

If your Macintosh runs MacOS 8.6 or later and has at least 64MB of
memory (RAM), you can avoid this problem by installing Netscape 6.x or
the current Mozilla.

If your Macintosh is not capable of running the more modern browsers,
you can continue to use Netscape 4.x by configuring it to use a
shortened version of the automatic configuration script at URL

http://proxy.lib.berkeley.edu/small.pac
(for the conventional PIN-authenticating proxy server) or

http://proxy.lib.berkeley.edu/smcalnet.pac
(for the CalNet-authenticating proxy server). If the resources you need
are not available via these shortened configuration scripts, please
submit the Proxy Server Problem Report Form and we'll try to
accommodate your needs.

NOTE: I don't file Proxy.pac on my computer, thus, I don't a proxy
because you need that file to run a proxy.