In order to download from this website you will need TS3 INSTALL HELPER MONKEY.
You can only get it here:

Once you have done this, all you have to do:
1. Save your download to desktop
2. Right click and select install with monkey helper
3. After it creates a folder, open folder and select the file with the monkey face.
4. Go to the top and click install to Sims 3
If you need any other help please feel free to explore the help page from MTS 3