If you're going to run self-hosted WordPress, or self-hosted anything, you should learn to use FTP. While you can skate by without learning much about Databases, FTP will save your bacon 9 times out of 10.
There's a Codex page on FTP clients: http://codex.wordpress.org/FTP_Clients - If you're on a Mac, try CyberDuck. It's free and pretty easy :)
Basically you're going to FTP to your server, navigate to the wp-includes/ folder and upload the file I linked to.
It's not much harder than copying a file from one folder to another on your computer. Once you log in, it's generally straight forward.
Alternately, you can upgrade to the 2.9.1 Release Candidate, which fixes this (and other things). See http://wordpress.org/development/2009/12/wordpress-2-9-1-release-candidate-1/