For a dual-boot machine (where the main desktop would be Linux), a common 'data' partition makes sense (rather than allowing root access by Linux to the Vista install, or visa-versa).
Since the Vista driver requires it, you need to format the shared 'ext3' partition with :
/sbin/mkfs.ext3 -I 128 /dev/sd_A_
The Vista driver seems to overwrite the UID of the partition. This means that if the UID is used in /etc/fstab to define the mount-point, and the parameters are set to mount it at boot time, then you can get dropped into a very unhelpful boot-fix shell ("Good Luck!").
Use the following to remount the root partition as read-write (so that /etc/fstab can be altered and saved) :
mount -w -o remount /
Best solution is to reference the drive by its 'LABEL' - use '/sbin/e2label LABEL=nameofdisk' to do this, and adjusting the line in /etc/fstab to match. (Do this before ever mounting it in Vista)
Ext3 Driver for Vista
I found that the one at fs-driver.org works just fine on Vista32. It seems to 'just work', and the latest features even mention that it takes care of
ext3 journals. Niiice.