When I set up 9.04, with the help of a friend, I set up a custom kernel and was wondering if I upgrade to 9.10, will have to redo the whole kernel or will it keep the same kernel.
Thanks.

Upgrades usually go with the next stable kernel for the release.
You should be able to upgrade everything without having to rebuild the kernel.
I's check the ubuntuforums first.

I've tried but 3 days later, still no reply. Ubuntuforums.org sometimes doesn't like to answer questions that they think are worthwhile i guess?

Try the mailing lists next.

Upgrading will generally put a newer kernel on your system, but you can still choose the old kernel from the grub menu and it should work. What do you need a custom kernel for anyhow? It's possible the newer Ubuntu kernels might support the functionality you needed in the custom kernel.

Well, I'm using a 7 year old computer, so the kernel is built for that.

That's hardly an argument. Older kernels have more bugs and vulnerabilities. My main desktop machine is also seven or eight years old and has no problem running a current kernel.

The only thing to consider is when you have 3rd party drivers, like the ati or nvidia ones. The latest kernel might not be always supported by these, but that doesn't seem to be your case.

Oh ok, well, my friend that helped me build just said that would be best, so I didn't know. How can I find out if the new kernel would suffice for my machine?

Try it and see.

If the old kernel works, the new one will work as well. Updates add features, very rarely remove them.

There could be some manual configuration needed though. For example, if you have IDE drives and your old kernel is using the old IDE drivers, and the new one uses the PATA drivers instead, then the names of the drives will change from hda, hdb... to sda, sdb and so on. That can require some fixing in /etc/fstab and probably grub.conf (or lilo.conf or whatever you are using).

But you really should stay up to date, using the last stable version of either 2.6.x or 2.4.x, unless there's a true reason not to (like a conflict with closed drivers, as said before).