Problem: Getting the G1 to mount as mass storage device to Windows VISTA; When windows can not find the driver.
TRY THIS FIRST
Solution found here - http://teknobabble.wordpress.com/2007/08/18/vista-driver-problems-installing-a-usb-media-reader-a-solution/
To get vista to look where you want to for the driver after you follow the steps at this link.
Right Click Computer/ Properties/ Device Manager/ find the device with the question mark next to it right click and Update Driver software.
Browse / and point windows to search in C:\Windows\inf
ONLY TRY THIS AFTER YOU TRY THE OTHER. (borrowed from the poster above.)
Additional Info - If for any reason the first link dosent work try this. On your phone go to Settings, then Applications, and then Development. Unselect the checkbox for "USB debugging", Connect the phone to your computer and you should receive a notification on the phone that says "USB Connected". Select to Mount and you should be able to see the contents of the SD card on your computer.
If that doesn't work try these drivers:
http://dl.google.com/android/android_usb_windows.zip