UPDATED!

These methods can only be done on RC29 or lower. If you are already on RC30 (RC8/UK) you must first downgrade to RC29 using the leaked firmware and get the root access that you seek to keep.

So if you are already at RC30 (US) you need to do this first:
http://www.androidfanatic.com/cms/community-forums.html?func=view&catid=9&id=219

OR

if you are on RC8 (UK) you need to do this first:
http://www.androidfanatic.com/cms/community-forums.html?func=view&id=220&catid=9

With the help of JesusFreke we have sourced a pre-modified version of RC30 (RC8/UK) that you can use if you do not wish to manually edit it yourself.

If you copy files over USB to /sdcard remember to unmount before unplugging the USB.

1. Download the modified recovery image

AndroidMod1.0 .xxx file G1 downloadable link (rename to .zip)
http://www.megaupload.com/?d=WCNUWT47

2. Unzip the file and copy (or adb push) recovery_testkeys.img to /sdcard

3. Download the modified update (Do not unzip it!)

US VERSION

JesusFreke's RC30 v1.31 .zip file Non G1 download, no need to rename
http://www.megaupload.com/?d=CKJ4XT8R

UK VERSION

JesusFreke's UK RC8 v1.31 .zip file Non G1 download, no need to rename
http://www.megaupload.com/?d=MRSH49IO

4. copy (or adb push) this file to /sdcard/update.zip - Make sure that if you copy over USB that you unmount before unplugging

tip: If you are on windows, and have the hide file extensions for windows option turned on, once you rename the file to update.zip, make sure you only see update, and NOT update.zip. Because if you see update.zip, it means that it's really named update.zip.zip, and the phone won't be able to find it.

5. Copy the recovery image to the /system partition:

with a root run:

1. mount -o remount,rw /dev/block/mtdblock3 /system

2. cd /system

3. cat /sdcard/recovery_testkeys.img > recovery.img

4. flash_image recovery recovery.img

Now You must

6. Turn off phone

7. Turn back on the phone and let it boot normally (don't go into recovery mode yet)

8. Once the phone finished booting, turn off the phone again (yes, you really should let the phone start up normally once. Don't skip this)

9. Hold down power and home to enter recovery mode

10. At the exclamation point and phone image hit Alt-L look for test-keys on the second line. If missing, the above steps failed and you should hold Home and Back to reboot and start over. If not, continue.

11. Press Alt+S. The system will proceed to verify the image and install it. When done, it will say to reboot by pressing Home + Back.

12. Press Home + Back. The system should show an open box and arrow into phone, then an arrow onto a chip, then reboot twice.

This will give you an rc30 that has 'su' for gaining root access.

This has been successfully tested, but as always, perform these steps at your own risk.


Thanks to DarkriftX at http://www.android-dls.com

what about if ur on rc33?

.
Just install JF's modded RC33 Firmware instructions and download here:
http://www.androidfanatic.com/cms/community-forums.html?func=view&id=2245&catid=9