It is easy to install Opera on your Centos 5.5 system, just follow these steps:
– Go to http://www.opera.com/browser/download/?custom=yes and pick your flavour
– download the file
I picked the 64 bit version and had to execute the following lines:
yum install gstreamer.x86_64
yum install gstreamer-plugins-base.x86_64
yum install gstreamer-plugins-good.x86_64
rpm -Uvh opera-10.61-6430.x86_64.rpm
opera