confusing .. I know .. I've been through it myself recently on Apache2 and IIS .. but normally it isn't this difficult ..
for a windows installation use the backward slash notation c:....\
extension_dir = "c:\php\ext\"
NOT extension_dir ="c:/php/"
don't know where php5 crept in in installation but you'll have to decide which to use .. c:\php\ or c:\php5\ ..
then (if the simple c:\php) .. to be consistent .. change all occurrences of c:\php5 to c:\php
to be safe search throughout disk to locate c:\php5 and change to c:\php
http://www.agentransack.com is a good search utility for file search
but also you might search registry .. Start | Run | regedit .. Edit | Find .. c:\php5
..
also have you downloaded the PECL library ?
see separate "collection of PECL libraries" here (not included in PHP5 binary download)
http://www.php.net/downloads.php
..
to button this down .. if php_ldap fails to load .. after the above changes, download FILEMON from http://www.sysinternals.com
run filemon .. setup the exclude filter in filemon to exclude all background running processes until you see an empty window (first time usage the window is full because wildcards are used) ..
then setup the include filter to monitor simply ... php_ldap
shut down IIS server
restart IIS server
and inspect filemon window to see what happens when php_ldap.dll is attempted to be loaded
..
to test your PHP installation outside IIS you could try a very simple personal server from http://www.badblue.com .. which runs PHP in a matter of minutes from first installation .. then migrate to IIS when the PHP bugs are ironed out.
install on some port like 8080 (not 80 if IIS is running).