for windows it might be better to just get the setup at http://gnuwin32.sourceforge.net/packages/openssl.htm
instead of the sources and try to compile 'em yourself ^_~
In order to use the OpenSSL functions you need to install the » OpenSSL package. PHP between versions 4.0.5 and 4.3.1 will work with OpenSSL >= 0.9.5. Other versions (PHP <=4.0.4 and >= 4.3.2) require OpenSSL >= 0.9.6.
You are strongly encouraged to use the most recent OpenSSL version, otherwise your web server could be vulnerable to attack.
for windows it might be better to just get the setup at http://gnuwin32.sourceforge.net/packages/openssl.htm
instead of the sources and try to compile 'em yourself ^_~