Background: I have a kubuntu laptop right now that I can't use wirelessly, i.e. I haven't got wireless assistant installed. But I have a windows laptop that I can download the debian packages seperately on a USB memory stick.
How do I install a debian package on the computer locally?
Can you just not point the package manager to the location on the memory stick?
Once you have the USB stick mounted:
dpkg --install /path/to/foo_VVV-RRR.deb
(where fooVVV-RRR.deb is the package's file name)
You can find more commands at the Debian GNU/Linux FAQ.
Side note: this is from the command line. I'm not sure how to get synaptic to do it.
If you're not a command line fan, double-clicking on the .deb files in the file manager should launch a package installer. Has exactly the same effect as dpkg -i of course.