you're just confused because you're used to a different phone, it's normal, welcome to the Droid X! To flash a ROM you need to make sure you are on the same kernel that ROM uses, so if you are on .602 then you need a ROM that uses the .602 kernel. All you need to ROM Manager and Clockwork Recovery (same app) and you can flash any ROM on the right kernel. I would recommend MIUI or Shuji, the battery life and stability are the best in my experience.
Here's a really informative thread for you to look at to understand better:
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