I could have downloaded Google Desktop in .rpm or .deb format for ease of installation, but decided instead to go with the repository approach. I chose this approach in order to get automatic updates, and also to make it easier to install other Google software that might interest me. There were a couple of repository options. Before taking the manual approach to the repositories, I decided to try Google's automated installation script. To run that script, I entered these two lines into Terminal, as instructed:
wget https://dl-ssl.google.com/linux/google-repo-setup.shThat caused Ubuntu's Update Manager to fire up and offer to install a bunch of software updates. I gave it my consent to proceed. When it was done, I went into System > Administration > Synaptic and searched for google-desktop. I marked google-desktop-linux for installation and clicked Apply. Now I had a new Ubuntu menu item, Applications > Google Desktop. I went into that and clicked OK, or whatever it was.
Now I noticed I had a Google Desktop icon in the system tray, or whatever they call it in Linux -- in, that is, the bottom right corner of the screen. I right-clicked on that and set my Preferences. In Preferences, I typed in "/media" as a folder to search, since I had some Windows XP partitions with data there. Now the hard drive began churning away, presumably indexing the stuff in those partitions.
While that was doing its thing, I went back into Synaptic, searched for google, and clicked on Package, to arrange the options alphabetically. I installed googleearth. I noticed a google-chrome-beta, but decided I didn't need it right now.
I tried using Google Desktop. It only searched the web. I right-clicked on the system tray icon and changed the default search type to Desktop. I was searching for "command economy." It didn't find anything like that on my desktop. I right-clicked on the icon again and chose Index > Index status. It said it was only about 15% done with indexing, so I let it go for a while. But when it was done, it had catalogued only a small number of my total files, so I guessed that it was not cataloguing subdirectories in /media. I went into Google Desktop Help for Linux and searched around. I didn't find an answer, so I posted a question. Ultimately, I solved this (and other difficulties arising from 64-bit Ubuntu by downgrading to 32-bit Ubuntu.