There is an app in the Market called "Droid X Recovery Bootstrap". Download and install this app from the market (make sure you are rooted first -- there is an app called "z4root" that will help you root).
Run the Bootstrap app. Press the "Bootstrap Recovery" button and accept any Superuser alerts that pop up.
Then, press the "Reboot Recovery" button. Follow drod2169's ROM installation instructions to the letter from there.