How can I install XFCE along side Unity?

There are no conflicts between XFCE and Unity, and Nautilus works perfectly fine on Xubuntu 12.04 and 12.10.

If you wish to install XFCE in Ubuntu, install either xubuntu-desktop (for XFCE + Xubuntu branding + all Xubuntu default apps), or just xfce by itself if you don't want to end up with two sets of default apps.

sudo apt-get install xubuntu-desktop

or

sudo apt-get install xfce4

Additionally - and I stress that this is based only on my own personal experience on one laptop - I've found that Xubuntu boots and runs much more quickly than Ubuntu whether Unity is installed or not. Based on this experience, I always prefer to install Unity on Xubuntu instead of XFCE on Ubuntu if I want an OS with both desktop environments. You may wish to try the same next time you reinstall your OS and see if you notice any performance improvements.

Just install xubuntu-desktop and it should work :). It should not conflict anything (never did for me).