As Mentalist Traceur said, just use flasher -f -k <zImage> -b either the stock kernel (if you still have the stock kernel headers installed -- I don't.) or extract a zImage from kernel-power-bootimg or kernel-power.

As for the root user problem, remove rootsh and sudser, and reinstall them using FAM/HAM.
Also, you can't gain root when you're already root. Are you sure you aren't already root?