Ilia Alshanetsky has posted a quick note about building PHP with cURL/HTTP support combined with adding a MySQL extension. Conflicts can happen with some of the libraries, and he knows how to solve it.
The MySQL binaries found on mysql.com are built against yaSSL as opposed to the more common openssl against which libcurl (usede by cURL and HTTP extensions) is linked. The conflict between the two libraries causes curl initialization of the SSL layer to fail preventing startup of the PHP extensions.
The fix? To either use the older mysqlclient libraries or manually compile MySQL yourself against the OpenSSL libraries.