I'm using xubuntu on an old PC. I've installed it with the Alternate CD, but it only installed terminal. I need to install xfce but when I do apt-get install xubuntu-desktop, it tells me to insert the CD. I insert the CD, it copies some files, both from online and from CD, then it gives me a bunch of CD errors and says that the md5 check failed, along with some sector read errors or something. Is there a way to disable the use of the CD for a package source and just download everything from the Internet?