You can run these commands to install PECL memcache (not memcached).
However, this memcache will work with memcached.
wget http://pecl.php.net/get/memcache-3.0.8.tgz
tar xvfz memcache-3.0.8.tgz
cd memcache-3.0.8
phpize
./configure
make
make install
Take note of the php extensions directory that memcache is installed in.
Mine is: /usr/local/lib/php/extensions/no-debug-non-zts-20020429/
Then add this line to your php.ini
extension="/usr/local/lib/php/extensions/no-debug-non-zts-20020429/memcache.so"