From what i have been told you go to your files.
Click on Ea games.
Then Sims 2.
Make a new folder, label it Downloads.
Go to google and type in mod the sims 2
When your there sign in or sign up.
There should be boxes, click the one that says downloads (obviously). :D
There should be a search engine, type in what you want.
Click on what you want, something should pop up ( it will be downloading).
Click save, find your folder and save it in there.
Right click it, and it will say extract here or something. (Sorry not that sure)
Play your game and click the custom content button, and you should be good to go.
I got this information on *youtube*
If you want you can just go to youtube and look up (Sims 2 custom content download).
Hope i helped. :)

i never could get mod the sims2 to work so i go to www.thesims2.ea.com and there u can download 1,000's OF SIMS ! and cars =D hope u have fun there ! ill find
more sites and tell u more late