If you want to install the rooted GB flash, you need to SBF back to Froyo and turn on airplane mode first. Or you could possibly run into what I did....
I SBF'd back to Froyo, but before I could root and reboot to recovery, the OTA .596 update came up and asked me to install. I hit later, rebooted and wiped data and flashed the .596 rooted zip. So I then boot into GingerBread, and the damn OTA update started coming up again even though I was on .596 already!
So I did another SBF, turned on airplane mode and prevented the update check. This may not happen to everyone, but it did to me so just warning you.
When I decided to go with a custom rom, I started with a sbf. I wanted to have a "clean" device to start with. You should. IMHO, also do the following:
Make sure you wipe cache(s) AND factory reset before leaving recovery. When you reboot there are no remains from previous installs.
After I SBF'd back to Froyo I rooted, installed D2 bootstrap, then the TBH pre-rooted 2 part. Also wipe and factory reset and davlick wipe before reboot.
If it asks for OTA update before you get to install the 2 part, choose cancel or later. That info will be gone when you wipe/factory reset and never ask you again.
Wait to sign in to your google account, if you have one, until after you're up and running the 2 part. It's pointless to do it before.
My DroidX Thrives on the DarkSlide!!