Memcached is a memory caching system. This will help to increase speed of your vbulletin or wordpress wesites. You can install it easily as follows,

Download the memcached server from http://memcached.org/

wget -c http://memcached.googlecode.com/files/memcached-1.4.5.tar.gz tar -xzf memcached-1.4.5.tar.gz cd memcached-1.4.5/ yum -y install libevent libevent-devel ./configure --prefix=/opt/memcached make make install

Now install init script . I wrote an init script for redhat and centos servers , you can use it to start/stop memcached.

wget -c http://files.syslint.com/conf/memcached.redhar.rc.txt mv -f memcached.redhar.rc.txt /etc/init.d/memcached chmod 750 /etc/init.d/memcached mkdir /var/run/memcached /etc/init.d/memcached start chkconfig --add memcached chkconfig memcached on

Install php-pecl memcache
Download the latest stable memcached from http://pecl.php.net/package/memcache

wget -c http://pecl.php.net/get/memcache-2.2.6.tgz tar -xzf memcache-2.2.6.tgz cd memcache-2.2.6/ phpize ./configure make make install

Now restart apache and create a phpinfo page and test whether the memcache options is showing or not. If it is there then you installed php module . If not you need to check your php.ini settings and enable memcache module