Next step before doing anything else is to install rom manager, use it to flash clockworkmod recovery, and then use rom manager to do a backup of your existing rom. You can do that when you attempt to isntall a custom rom, but I'd do it by yourself.
That's good to have regardless (the backup). And if you were to "brick it" you shoudl be able to boot into recovery (power+X key held down) and launch nandroid from there, and restore the rom.
But before I'd try to flash a rom, I'd really do some research in droidforums and androidforums, because the more I think about it, the less likely I think it will work. You are using a Droid, BUT on a different carrier. And all of those roms are designed for verizon. My gut says it won't work.
Indeed, you might look for threads on kernels, and not roms; because its possible (and I am totally speculating here) that you might be able to flash a kernel to an existing rom, but man, I just don't know enough about the technology to say that with any certainty.
