I would add to Mike Kaganski's answer that the SI-GUI depends on Microsoft's .NET being installed to the system. (The SI-GUI installer will automatically ask if you want to download and install .NET) If you don't have, and don't want, .NET on the system then it is possible to do a manual parallel install of LibreOffice.
The instructions on how to do a manual parallel install can be found here: Installing Several Versions of LibreOffice in Parallel. The instructions look a bit complicated but in practice it is easy to do.
In the parallel install instructions for Windows - under the heading User Configuration - only one option for where to store the User Data for the parallel install is given. However, several options are possible for editing the bootstrap.ini file - those other possibilities can be seen here under the heading bootstrap.ini: http://dev-builds.libreoffice.org/si-...
Also in the manual install instructions it is implied that the user should launch the parallel install LibreOffice only via soffice.exe. However, it is safe to directly launch whatever component of LibreOffice you want to use e.g. sdraw.exe, simpress.exe, swriter.exe etc. Whatever component you use LibreOffice will always read the bootstrap.ini file for where to read/write user data/settings.