Sims 2 : I prefer to use the Clean Installer, open the house with the CI [Clean Installer] install first the house without contents. Start your game and go afterwards out of your Game. Now you should open the house with the CI again and install just the content without the house. Its a bit complicated but that helps, it can be the house dont show in the catalog and thats annoying!
Sims 3 : Double click on the house it opens the Launcher click on install - thats it!
But if you have trouble with the Launcher [like me from time to time] then you can put the sims 3 file direct in the Download Folder [Documents / Electronic Arts/Sims3/Download].Thats an easy way too.Test it!
You may send me an email if you have any question about to install the houses, but pls accept if you write a question as comment under a house ill delete it! Use the email button on the home site - thanks!