mkdir /var/pecl-install
cd /var/pecl-install
wget http://pecl.php.net/get/Fileinfo-1.0.4.tgz
tar -zxf Fileinfo-1.0.4.tgz
cd Fileinfo-1.0.4
phpize
./configure
make
make install
cd /var
rm -f -r pecl-install
http://jeffreybarke.net/2009/02/installing-fileinfo-module-on-media-temple/