Firstly, you can just run Nautilus as root from the command line with:
gksudo nautilus
The following procedure will add a root file browser to the Applications | System Tools menu.
I got this from http://ubuntuforums.org/archive/index.php/t-256998.html.
Create a text file with:
gksudo gedit /usr/share/applications/Nautilus-root.desktop
Add these lines to the file:
[Desktop Entry]<br />
Name=File Browser (Root)<br />
Comment=Browse the filesystem with the file manager<br />
Exec=gksudo [...]
