You should setup the new repo by adding the .repo file to your system.

Centos 5 and 6 are very similar.

Run through the following steps as root:-

1. cd /etc/yum.repos.d/
2. wget -c http://download.opensuse.org/repositories/home:/oojah:/mqtt/CentOS_CentOS-5/home:oojah:mqtt.repo
3. yum update

You will be prompted if you wish to install the packages, answer yes.

If you should see the following message. You should answer yes.

Importing GPG key 0x49E1D0B1 "home:oojah OBS Project <home:oojah@build.opensuse.org>" from 
http://download.opensuse.org/repositories/home:/oojah:/mqtt/CentOS_CentOS-5/repodata/repomd.xml.key

You may see the following warnings:

useradd: unknown group mosquitto
warning: user mosquitto does not exist - using root
warning: group mosquitto does not exist - using root

They can be ignored or you can manually create the missing user group details. You should then edit the file /etc/mosquitto/mosquitto.conf to suit.

Finally start mosquitto as a daemon with the line, /etc/init.d/mosquitto start

And that should be it!

The Fedora steps should be very similar to Centos steps but didn't have a machine to test it on.