First & Foremost, go into the Bootstrap app & make a complete backup.
Hit "Bootstrap Recovery," then hit "Reboot Into Recovery" (This takes you to "Clockwork Recovery".)
Once in "Clockwork Recovery," your gonna use the "Volume Hard Keys" to scroll down to "Backup and Restore." Then use the "Red Camera Button" to hit "Backup...."
This will make a complete backup, just in case, and its always good to have a "Stock Backup".....
Now, on to installing a Rom....
This is pretty easy....
Your gonna want to Download the Rom of your choice, from your phone, onto your SD Card.
Then go back to the Bootstrap App.
Once again, and like you always will, hit "Bootstrap Recovery." Then hit "Reboot Into Recovery."
Once again you'll be in "Clockwork Recovery..."
Now use your "Volume Hard Keys" again to scroll down to "Wipe Data/Cache," and use the "Red Camera Burton" to hit that (this is a must when installing a Rom for the first time & most other times as well.)
Now scroll to "Install From SD Card."
Pick the exact file you downloaded onto your SD Card earlier. Hit "Install."
Now let it work its magic.....
When its done, reboot your phone....
Don't worry if it takes long to reboot. I've had it take up to 10 mins to reboot my phone after installing a new rom....
Hope this helps-
Swyped with my Droid X! Flying with Liberty & OC to 1.4 Ghz