Copied from the link in Op
2. Put phone into bootstrap recovery
3. Install the file you downloaded above
4. Sit back and watch (Your phone will bootloop for approx 30 secs, if any longer than that, pull battery and restart your phone.
You should now have gingerbread and it should be rooted.
5. You have to use D2 Bootstrap on Gingerbread, DX bootstrap won't work.Get it here
Droid 2 Recovery Bootstrap v1.0.0.3.apk You might get DX bootstrap to work if USB Debugging is off
6. If you're having Sync Issues After flash you need to Go back and do a Factory Reset in Stock Recovery. It helps if you do it multiple times. I usually do it 3 or 4 at a minimum.
7. IF YOU FOLLOW P3Droid ON TWITTER YOU ALREADY SAW THAT IF YOU WANT TO KEEP ROOT THEN YOU SHOULD NOT EXCEPT THE OTA.
TO HELP THAT NOT HAPPEN RENAME UPGRADE.APK TO UPGRADE.BAK IN /SYSTEM/APP
8. Apps missing from your market? Here's an easy fix compliments of JRummy. Get it here.
http://dl.dropbox.com/u/14119868/fix.apk