Is there a package readily available that can replace & enhance the functionality of Nautilus?
Midnight Commander! Just type mc from any command prompt.
Thunar is a decent light weight replacement.
While it has a few peculiarities, I've had mostly positive experiences with ROX when I've had a need for a graphical file manager. It's much lighter than nautilus.
I love mc, and wouldn't use anything else. But, if it's too 80's for you, you can get gnome-commander from the repos.