If I install any desktop environment (like XFCE) alongside Unity can it affect Unity?

I want to be sure whether it going to break something like my default Unity desktop or not. I once tried KDE on Ubuntu and it broke the whole theme. I had to reinstall Ubuntu that time.

I dont want that to happen again.

I have found this which explains how I can Install XFCE or other DEs Available for Ubuntu 11.10.

I have them both installed right now. I just logged out and back in on both DEs. I have KDE, XFCE, Gnome fallback, and Unity installed for testing purposes. Aside from occasional cluttered menus and file associations, it works fine for me.

There is no one true answer to this question, since it depends on the environments you want to install on one system. I currently have unity, gnome-shell, gnome-session-fallback and awesome installed and they get along fairly well, which makes sense since the first three are pretty much the same (configuration and application-wise) and awesome does not share any settings with the former or bring in any other applications.

You just have to know that there might be some caveats to running multiple DE's. For example installing gnome-shell will overwrite unity keyboard shortcuts.

You won't run into major (think unusable system) Problems, but installing xfce will pull more than just the DE, like the suite of standard xubuntu applications. This means that your System will be filled with unnessecary redundancy.

That being said, xfce can be installed here:

Click to install