Whenever I try to install something (like flashplugin-nonfree), it says:

Media change: please insert the disc labeled
 'Kubuntu 11.04 _Natty Narwhal_ - Release amd64 (20110427.1)'
in the drive '/cdrom/' and press enter
This is very irritating. I also encounter the problem where every time after I perform (or attempt to) perform an apt-get operation, and wish to perform another, I get this:

E: Could not get lock /var/lib/dpkg/lock - open (11: Resource temporarily unavailable)
E: Unable to lock the administration directory (/var/lib/dpkg/), is another process using it?
Anyone out there know of a solution to this? I'm running Kubuntu 11.04.