Droid 2 Verizon 2.3.4/4.5.621 help?

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http://androidforums.com – Just received my first droid phone the other day. I reset to factory, then downloaded all of the updates from Verizon. I later read that you shouldn't root the phone if you've done all of the updates through Verizon because it'll brick the phone. I'm new to the lingo and using ROMS. I want to use this phone to learn though. Can I revert back to an earlier version of the UI, then root and install a custom ROM, or have I stuck myself with a stock phone. Suggestions, links to guides, anything would be a help at this point. I can't seem to find the answers I've been looking for. Hardly anything o (General)