Re: 256-series drivers won't install on Kubuntu with 2.6.32-24 kerenel (AMD64)
Please read the sticky regarding how to report problems and provide a nvidia-bug-report file as described there. (Of course only when the problem occured, therefore you have to boot the newer kernel. As you can have multiple kernels installed and choose in grub which one to boot, this should not be an issue)
Even though manual driver installations in Ubuntu are not what I recommend and probably the problems are related to this, I am not aware of any problems with this combination and I never heard of it in the ubuntu support forum I am supporting in.