I was going to upgrade my kernel to 2.6.15. I accidently installed the version for amd64k8 because it did say it was for athlon 64. Also I cant boot back into my old kernel. When I do it goes me an segmentation fault. Then it drops into busy box.

So I was wondering if I reinstall ubuntu without formatting the partition would files in my /home be erased? But I will have to install any apps I installed right?

If you can get Ubuntu not to format your /home during install, you are safe.

If you didn't delete the old kernel, you should be able to recover by using your Ubuntu CD in recovery mode or a live CD like Knoppix. Actually, someone more versed in Grub could probably help you do it without either of those...

I do have a koppix live cd. What can I do to recover my old kernel. Do I just rewrite the grub config file so that grub doesn't know about the new kernel?

I haven't used grub, but that's what I did with LILO. Just point it to boot the old kernel automatically. I'm not sure with grub, but I had to chroot to run /sbin/lilo after restoring the lilo.conf file. I get the impression you don't have to run anything to reset the primary boot loader with grub, so you should be able to just modify the grub config file and then reboot.

If you can get to the grub prompt at boot, try this

Type c to get into the config mode and type the following

root (hd<tab>,<tab>)
By hitting tab, you can select the appropriate disk and partition
kernel /<tab> root=/dev/hdxn
Check if you can get to the /boot and the appropriate kernel
x is the disk (a/b...) and n is the partition where you have / (the root partition)
initrd /<tab>
Pick up the appropriate initrd file
boot

yo thats cool didn't know u could hit tab to select the disk/ partition. I never come across a tutorial on grub that mensions that! THANKS!!

Why don't you want the k8 kernel? Isn't it the same as amd64 kernel except with more tweaks for spead? Do you not have a amd64? According to this thread, the K8 is designed for people with k8 motherboards, but i'm not sure if thats entirely correct or not. If that is the case, then why does Gentoo recomend you change your settings in your make.conf file to "-march=k8" if you have an AMD64 processor?

Note: They don't mention anything about motherboards in thier install guide, and Gentoo is the most well documented distro, correction, anything i've ever seen.

Of course I have an amd64 processsor but the k8 kernel doesn't seem to like my hardware it just boots to a blank black screen. Hence I assumed I installed the wrong kernel otherwise it would be working.

So after you bios loads and such, it just blacks out? Or your X server quit working? If I were you I'd try rewritting the grub.conf with the liveCD before I did anything drastic, you can remove the symlinks and then new kernel you don't work after you get it booted again.