When multiple need to be installed, a such option will be very useful.
What command should be put into a script in
Or in Nautilus-Actions Configurations Tool?
There already appears to be a script for dealing with debian packages on http://g-scripts.sourceforge.net/. See: http://g-scripts.sourceforge.net/nautilus-scripts.tar.gz file: nautilus-scripts/System Configuration/Debian_Package .
I haven't tested it, but reading through it, it seems to not be too bit-rotten. Compared to what you seem to want, it requires an additional step, as it creates a dialogue asking whether you want to install the packages, extract them, or get info about them. You could easily remove the extraneous parts, though.
If you would prefer to use something like gnome-terminal, rather than xterm, for the installation (to enter your password / view the output), you would need to replace
XTERMPRG=/usr/bin/gnome-terminal and the
-T flag on line 47, with