Luis,

When using Ubuntu 12.04 you should do the following:
- download SH3D 3.7 using the green button here or version 3.6 here.
- unzip the downloaded file.
- drag the unzipped directory where you want it.
- right-click the file SweetHome3D, choose Properties, then Permissions and make sure that you Allow executing file as program.
- ready.


Hans