I think there is some confusion on this forum between a rooted phone and one that has the leaks installed. They are not the same thing.You do not flash to V3 before rooting. That will prevent you from rooting.
You root straight from stock 1.5
There are ROMs built off of V3 leak so those are what you want. But just to be clear-once again- do not flash to anything if you want to root.
It does seem possible that you can root if you go from 1.5 straight to flashed OTA. Not LV3 but OTA. It is pretty much confirmed, but nobody has gone 100% through the process yet. I believe that will be tested and confirmed later tonight. So maybe you want to keep an eye on that and go that route. Keep an eye on this thread (below) tonight if you are interested in this route.
http://androidforums.com/htc-droid-eris/78458-attn-leakers-otad-not-1-5-otaers.html
And this thread
http://androidforums.com/htc-droid-eris/78619-went-1-5-ota-you-can-still-root-not-leakers.html
Otherwise just root right from 1.5
Rooted means you have administrative rights to the Operating System.
Installed leaks 2.1 v1, v2, v3 only take you to the next firmware level. You do not get administrative rights. It takes a special version of the release to get a rooted phone.
You cannot go from a rooted 2.1 v2 to a rooted 2.1 v3 simply by installing the 2.1 v3 update. You will end up with a 2.1 v3 that is not rooted.


Thanks hope this helps so confusion.