display_errors=ON --> 500 error

I've installed PHP 5.2.6 on my win XP, IIS 5.1 machine, and can get "phpinfo.php" to cough up the configure information like it should. Unless in php.ini I set display_errors = ON and error_log to syslog or c:\yada\yada.txt. In that case I get "PHP has encountered and Access Violation" in firefox (500 error in IE). I'd really like to see the errors php spits out to the log. I've set security in the file path so either "everyone" or IWAM_computername can read every directory above the last one, and IWAM_computername can read/write the last one. Doesn't help. What incantation will get error logging to work? (short of installing Linux. I share this machine.) Many thanks. Herb