Your iPhone/iPod must be jailbroken for Installous to be downloaded, assuming you've already done this we'll continue.
Installing Installous requires going into Cydia, so let's open up the Cydia app.
When you get into Cydia, go to the Manage tab on the bottom.
Click on Sources, this is where we'll add the Installous repo then click on Edit.
Click Add and type in the URL listed below
A warning will popup telling you that this repository has been reported by the community blah blah blah. Go ahead and click Add Anyway
You'll now see the Hackulo.us source in the list of sources.
Go into the Hackulo.us source and install the Installous 4 package. Once the installation is complete you will have successfully installed Installous onto your iPhone/iPod.