As you can see in the Ubuntu Releases Paragraph about Ubuntu on wikipedia, version 9.10 is too old (End Of Life) and is not supported anymore (even the server version).
You can find the repositories under the "old-releases" server http://old-releases.ubuntu.com/ubuntu/dists/
The first step here is to back up anything you could lose. After that, my opinion is that your best option is to clean install a new version and restore the backup.
If a clean install is not feasible
EDIT: Rereading the source links I noticed that the upgrade method
I've reported here could no longer work. I'll follow up once I know
EDIT2: The problem happens in the upgrade from 9.04 to 9.10 because both of them
are out of support, as discussed in this thread in AskUbuntu: Skipping intermediate Ubuntu OS upgrade to latest one,How do I upgrade from 9.04 to 10.04.2? .
Since 10.04 is supported I think the procedure below should be safe (but still risky)
The second best bet is to upgrade to a newer release (and you should do so as often as possible when a LTS version is released, in my opinion). It's important that you read about End Of Life Upgrades. What follows is taken from there, but not as complete as that page.
Since you haven't upgraded in time, you have some extra steps to follow.
Always do a backup, I've never tried this procedure myself, so try at your own risk.
First edit /etc/apt/sources.list like this to point the repository to old-releases. Notice that 9.10 (your current installed release) is codenamed karmic, so we use that. (if you have "backports" or "proposed" section of the repository activated, remove the "#" before their line)
## EOL upgrade sources.list
deb http://old-releases.ubuntu.com/ubuntu/ karmic main restricted universe multiverse
deb http://old-releases.ubuntu.com/ubuntu/ karmic-updates main restricted universe multiverse
deb http://old-releases.ubuntu.com/ubuntu/ karmic-security main restricted universe multiverse
#deb http://old-releases.ubuntu.com/ubuntu/ karmic-backports main restricted universe multiverse
#deb http://old-releases.ubuntu.com/ubuntu/ karmic-proposed main restricted universe multiverse
Update with the new sources
sudo aptitude update && sudo aptitude upgrade
Install update-manager-core if not already installed
sudo aptitude install update-manager-core
The installation of the following packages (server kernel) is also required
sudo aptitude install linux-image-server linux-headers-server
You can now upgrade with this command, as mentioned in the "Upgrading Ubuntu server" for the release 10.04 (this is the release after the one you have installed)
I suggest that before that you take a look at the Ubuntu server guide index for the release 10.04. Notice that even 10.04 is not the latest release, but at least is the lastest LTS and still supported.
Source on End Of Life Upgrades
Source for jaunty, the procedure should be similar