I upgraded from Kubuntu 7.10 to Ubuntu 8.10 this morning.
This was via a fresh installation into a new partition.
Getting it running went fairly smoothly but trying to get the NVIDIA drivers working was a world of pain.
It seemed that no matter what I tried I always got the following error:
Failed to load the NVIDIA kernel module
Every tip and bit of advice I found online didn’t work.
It turns out that the linux kernel headers aren’t installed by default but are required by the nvidia drivers (I only wasted two hours finding this out!).
It’ll never work unless you install the linux headers first.
These commands fixed it for me (exact version numbers may vary according to current Linux kernel version and your particular video card).
apt-get install linux-headers-2.6.27-7-generic
apt-get install nvidia-glx-177
Hope this helps someone.