Can be done easy with epel yum repo. more info about epel: http://fedoraproject.org/wiki/EPEL
for centos 5:
wget http://download.fedoraproject.org/pub/epel/5/i386/epel-release-5-4.noarch.rpm
rpm -ivh epel-release-5-4.noarch.rpm
yum install imagemagick php-magickwand php-pecl-imagick
restart apache and done
That’s all.