put those download files into C:\Documents and Settings\Administrator\My Documents\Electronic Arts\The Sims 3\Downloads,
then enter into game launcher, you will find exclamatory mark on download banner, which indicate uninstalled custom content,
install it then enter game.
you will see ur gorgeous house.
please make sure you have put the download house file in the right place, the C:\Documents and Settings\Administrator\My Documents\Electronic Arts\The Sims 3\Downloads, i mean.
then enter the game launcher
click the download button and select the house you want to install
click install
click ok button
enter into game and click edit town menu
dont forget to save your game
click show empty houses
select and click the house you just installed
select place copy
you can adjust the orientation to your satisfication
it is finished
dont forget to save or else you will find nothing there
do my best to make those i love & those love me happy...