Mac OS X gzips all your old system.logs. If you just want to find something in them quickly, you can use the "zcat" utility:
zcat /var/log/system.log.3.gzPipe the output to 'grep' and 'more' for searches and paging:
zcat /var/log/system.log.3.gz | grep sudo | moreType man zcat for more options.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20020515093217796