Step 1:
Get a microSD or SDHC card that is at least 500Mb and install it in your G1. For newbies: the slot flips open just below the green call button, you’ll have to put the keyboard up to see it.
Step 2:
Get a USB cable and hook your G1 into your computer. Slide the notification pane down and select the item named ‘USB Connected’ then choose ‘Mount’ from the popup options.
Step 3:
Download and install UBCDfix2.exe which I have re-hosted on this blog here. If you don’t trust me, an alternate location is listed on the pendrivelinux.com post. Run the EXE and extract the files to a folder named UBCD on your desktop.
Step 4:
Download the most current UBCD image. Here’s a link. Move it into the root of the UBCD folder you created on your desktop and pout the UBCDfix2 files in.
Step 5:
From the UBCD folder on your desktop, click fixubcd2.bat and follow the onscreen instructions.
DONE! You should now be able to reboot into your thumb drive. Be sure your motherboard both supports booting from a USB device and has the priority for that set above the normal hard drive. On a newer Dell, you can hit F12 to directly choose what to boot off of. Not only can you still save data to your thumbdrive from your G1 like usual, but you can get to all the stuff on your G1 via the UBCD you boot off of too.
Source – http://www.pendrivelinux.com/install-and-boot-ultimate-boot-cd-ubcd-from-a-usb-device/, http://blog.integrii.net/?p=173
