They could be almost anywhere. You need to find the httpd.conf file... in that file is defined where the log file is kept. Just do "locate httpd.conf" as a command in a terminal. The usual name for the acccess log file is "access_log". You could do "locate access_log". Mine are in:
/System/Library/RemoteAdminServer/Logs/access_log
/System/Library/RemoteAdminServer/Logs/error_log
There are many tools for processing the log files. Take a look on
http://freshmeat.net for lots of free tools for condensing the logfiles in to something useful.
Other handy thing is to run:
"tail -f /System/Library/RemoteAdminServer/Logs/access_log"
when you want to troubleshoot.
-DU-...etc...