1. Download this zip file: http://www.mediafire.com/?mi4utrhbacdbbxt mirror: http://www.megaupload.com/?d=LSR7QG9W
2. Rename it to PB31IMG.zip (uppercase name and lowercase extension matters, make sure it's not .zip.zip also) and push it to the root of your sdcard, so it's /sdcard/PB31IMG.zip
2 1/2. MAKE A NANDROID BACKUP (in case you ever want to go back)
3. Reboot into HBOOT by holding vol down while booting up, or by typing "adb reboot oem-42"
4. Hit vol-up when it asks if you want to apply the zip.
5. Wait for it to finish, then reboot when it asks you to.
Congrats, now you're back to stock 2.1-update1 with the original 1.00 radio.
thanks to aiccucs for his work in compiling the stock zip!