I am trying to install the non-OSE (closed version) and it says "please install the build and header files for your current Linux kernel". Now in the MCC it shows that a Virtualbox-kernel-2.6.17-13mdv.... is installed. And there is also a kernel-source-2.6.17.13mdv... Do I need to download the latter for the install? I am running Toronto.

Haha, I saw this question coming :-)

* Uninstall everything related to virtualbox
* Install: kernel-source-2.6.17.13mdv
(with urpmi or with rpmdrake so that all dependencies are installed too, that is make and dev packages)
* Download this version:
http://www.virtualbox.org/download/1.4.0/V...-1.i586.rpm.run
* Install it:
su
./VirtualBox-xxxx.run

Watch the output in the terminal!

* Maybe you need to add the user guest to the vbox user group afterwards.

Haha, you did ? Only a matter of time...I shall embark on this exciting adventure...

Success!! And you do need to add guest to the vbox user group.

Now, can I uninstall the kernel-source... file and gcc4 compiler? Or do they have to remain on the system?

You can unininstall it.