Yep - it was looking for a CD (or image) that wasn't where it was expected. I'm guessing you had the downloaded ISO image mounted to look like a CD (which is convenient) It's annoying but not fatal. If you want it to stop doing that, you can launch Synaptic, go to Repositories, and un-check the line that points at the CD. Or, if feeling adventurous, do this in the terminal:
Code:
sudo nano /etc/apt/sources.list
sudo we already discussed:
nano is a simple text editor, and the rest is the file to edit. Scroll down till you find the line with "cdrom" in it, and put a # in front of it on the same line. This serves to "comment out" the line, like the old DOS "REM" command. When done, hit Ctrl-O to save the file, hit Enter to accept the name), and Ctrl-X to exit to the terminal. Do another
sudo apt-get update afterwards to refresh the repositories.
Personally, I really like the apt-get system - it's one reason why I stick with Ubuntu, though I know other Debian-based distros have it too.