Please insert disk into E:How could he copy files to or from the G1 if Windows wouldn't recognize the file system?
jedman has the answer:
Plug in the USB cable to your G1. USB connected notification is on top of your G1 home screen, scroll it down. Click on the "USB connected" notification. Click "Mount." Go to your computer and select "Removable Disk (G:)" to access your G1 SD card. :)