any way to find history after deleted

From: erica (e_echo_five_at_yahoo.com)
Date: 07/28/03 

Date: Mon, 28 Jul 2003 04:27:10 -0700

I have reason to suspect some one getting on child
pornography web sites on my computer; I have no proof
because the person suspected denies all accusations and
also makes sure he deletes all history, internet cookies,
etc. Is there anything I can do? I've tried changing the
content setting on the control panel but some how he got
around the password. I would like to have some kind of
proof one way or the other, please help. I don't know too
much about computers.