http://www.if-not-true-then-false.com/2011/centos-6-netinstall-network-insta...
This is a tutorial that will guide you through and points to the correct URL for package repositories and to the correct install.img file.
Sure, but the install.img file at the package repository isn't more correct than the one on the netinstall CD. They are identical. The guy who wrote the tutorial obviously encountered the same problem but wasn't aware of the file on the CD and suggested this workaround.
I actually used this process several time and never encountered any issue of this type.
BTW, I got the system running. But I fear that I'll have to install
it several times again because I'd like to experiment with virtual machines and LVM. It's very likely that I break something since I have no experience with them. Therefore it would save me some time if I don't have to download a file which exists on the CD already.
For your time consuming concerned about breaking your VM, you can create one and then just clone it. This way you will always keep a fully working copy of your CentOS VM.
Another thing: Even if I can use install.img from the CD, at least
when I have to install packages, I have to specify an URL to a repository. Documentation proposes mirror.centos.org . Is there a reason why the installer doesn't offer the mirror URL as a default?
I ask because I have only one machine and whenever the installer asks me for an URL, I have to abort and boot a system which provides a web browser in order to read the documentation, write the URL down on paper, and start the installer again. Well, I sometimes have the impression that I'm the only one in the world who doesn't have a mobile phone with a built-in web browser. :)
For the default settings about mirror.centos.org it is beyond my scope ;)
Maybe not by default but an option stating "Do you want to get the sources from an official CentOS mirror". But anyway, mirror.centos.org isn't the hardest URL to remember.