I am using a new imac with osx lion 10.7.5 and have bought a copy of Apple iLife 11 on dvd a so that I can install iWeb and idvd, when I click on install iLife I get a message saying "iLife.kpg was signed with an invalid certificate

I am using a new imac with osx lion 10.7.5 and have just bought Apple iLife 11 on dvd so that I can install iWeb and iDVD, as macs no longer ship with these apps. When I click on install iLife I get a message saying "iLife.kpg was signed with an invalid certificate.

Next problem is that when moving through the installer and get to custom install, as I only want to install iDVD and iWeb, I am presented with the option to install iDVD, Sounds & Jingles and iWeb, but not sure what is going on with the other 3 options iLife Support etc, they seem to be greyed out but still look like they may install over the top of the newer versions already on my imac. Is it ok for me to just go ahead and hit install? Or do I have a problem?