This is from existz/untermensch's thread. I take no credit. See here for more info http://forum.xda-developers.com/showthread.php?t=909213
Making this modification will allow you to flash un-signed .zip files due to signature verification being turned off. (3e requires root)
* Download and extract the .zip
* Use a terminal emulator or ADB Shell and mount system as read/write.
* For backup purposes, use adb or root explorer to rename the current recovery file in /system/bin to recovery.orig
* Use a file manager (Root Explorer) and copy the new recovery file to /system/bin
* Reboot and your 3e (Froyo stock) recovery will no longer require signature checking.
You can now use this recovery or use the CWM from Captivate (posted in another thread here).
I am not responsible if this bricks your phone. This is easy cheese...just follow these steps.
3e Recovery w/o signature verification
Youtube video using Root Explorer from gtg465x (Make sure to Thank him!!)