I use
http://www.mandrivauser.de/smarturpmi/ because it will also package your selection in a .sh file for convenience. But remember to enter the following command in a console as root
urpmi.removemedia -a
before any new ones are added.
But you seem to have enough answers on this already.
I responded over the kernel and source with nVidia problem.
I have an nVidia Ti4200.
1. The 2.6.17.6 kernel that comes with the distro is out of date with some important fixes on later issues.
2. I have never found a kernel for 2.6.17.6 with a good signature - but I could have been unlucky.
3. I have installed and used the nVidia driver 9631-1 with both 2.6.17.7 and 2.6.17.8 with total success.
kernel-2.6.17.8mdv-1-1mdv2007.0
kernel-source-2.6.17.8mdv-1-1mdv2007.0
But I am curious as to why you do not use the Control Centre to install. It works fine after urpmi changes (and you can check those changes). And best of all, once you have a viable kernel and source installed and have booted up using those, it will install the nVidia driver without all that changing to run level 3 and stuff. Just make sure you follow the instructions that come at the end of installation.