Tuning store_avg_object_size

Hi,

I've been running squid for a few months now with a pretty good
improvement in bandwidth usage and surfing time for my LAN, but I've
decided it's time to go through squid.conf and tune everything I feel
safe touching (my cache is on a 486, it needs all the help it can get
:) ).

I was wondering if there's a way to determine the actual average
object size, using the objects that are currently in the cache, to
set the store_avg_object_size parameter?

As well, I can't seem to get the cachemanager cgi running, and I was
wondering if anyone has a webpage with a short walkthrough on getting
it running, or could perhaps walk me through the steps required. I
followed the instructions in the squid FAQ
(http://squid.nlanr.net/Doc/FAQ/FAQ-9.html), but I'm still unclear
about where the actual username and password is configured, and so I
can't log in to it yet. :)

Any and all help is appreciated,
Graeme

-- 
"It really is coming down to just Apple and IBM. If, for some reason, 
we make some giant mistake and IBM wins, my personal feeling is that 
we are going to enter sort of a computer Dark Ages for about 20 
years."
Steve Jobs, Playboy February 1985