For USB devices, you can use the following command

lsusb

but you'll need to have the usbutils package installed. On Debian based distros

apt-get install usbutils

will do the trick, but you might need to search with "lsusb" as a keyword if you have a non-Debian distro.

Once you've found out the chipset and pertinent information you want to do a search with something like "linux" and the chipset information in your favorite search engine. If I were searching for my usb/serial dongle, I'd search for "linux FTDI FT232BM". Usually you can find some HOWTO or newsgroup posting where someone has gotten the same hardware working or maybe they have failed and they give some indication as to whether someone is currently working on support for that device.