You are probably using the predefined common or combined log file format at the moment. You could do a custom format by selecting the fields you are interested in from
http://httpd.apache.org/docs/2.0/mod/mod_log_config.html#formats Many of the loggable headers are predefined (%...h is Remote host, %...H is request protocol, etc.) but you can get other headers out with
%...{Foobar}i (where {Foobar} is your header name) log format entries.
Follow the instructions for mod'ing your httpd.conf here:
http://httpd.apache.org/docs/2.0/logs.html