Changing the default "page not found" page?

[Spencer Gasson]

We are restructuring parts of our website at the moment moving it to
an improved directory structure and whilst I'm using some redirection
scripts I am concious that this probablly doesn't cover everything.

The error message that people get is just the default*.  I know there 
must be a way of changing this (and incorporating some elements 
to help me track down where the reference to the missing page came
from) but I wondered if anyone had done this or had some examples
on their site?

I'm keeping the enquiry general rather than technical specifically
because I also maintain pages for a number of professional and local
groups who I'd like to do similiar with, but they are run on different
ISPs.

All help appreciated,

Spencer
(who's working from home today, hence the address and enjoying
the sun)

* and by default I do mean the error message we haven't done anything
with it (dreadful I know).

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Spencer Gasson		http://home.freeuk.net/spenceruk/
Email:	SpencerUK at freeUK.com		    ICQ:	33650620	

" Typos exist in *your* state of mind and not in *my* reality. "