When you install Sonar X2 it will install in it's own folder. However, many folders are shared folders and the installation will update those files.
There is *never* a reason to uninstall a previous version of Sonar. There is nothing to gain by doing so. You only recover a few megs of HD space.
Rapture will install in it's own folder so you will have 2 versions installed. You will have the LE version and the Full version.
Dimension Pro is where it get's ticklish.
Dimension Pro 1.5 does not support DXi and will uninstall the DXi version.
This means if you have any projects that use Dim Pro you will have to reinsert Dim Pro and reselect your patches.