usually, finding an error involves knowing what time stamp to look for and finding that problem in the access and/or error logs.
many OS distributions include helpful tools, so you might want to explore that avenue.
i haven't tried it, but you might want to look at wtop and logrep. wtop - "top" for Apache and other webservers, plus powerful log grepping - Google Project Hosting: http://code.google.com/p/wtop/ [code.google.com]
i typically use general-purpose command line text processing tools to explore the log files like (e)grep, cut, sort, uniq, wc, etc. i also wrote a script i use to do certain types of analysis.