Also, check for items in the /Library/StartupItems or /System/Library/StartupItems folder (if the folder exists; it may not).
If you want to see where things are likely installed, grab a copy of Pacifist, find the installer on the Tiger DVD containing the Zinio Reader installer, and open it in Pacifist. It will not show you any files installed by scripts embedded in the installer bundle, but hopefully there aren't any.