Norm, I have not tested it on the others yet, but I believe it to be common for x86 not to have the x64 partition displayed in Computer. UPDATE:
Windows 7 (32 & 64 bit) cannot see Vista (64 bit) partition, but Vista 64 (bit) can see both Windows 7 partitions.
I believe the problem with System Restore Points being deleted when dual booting with XP and Vista played a part in this for Windows 7 to not be able to see Vista partitions. The solution to stop XP from deleting Vista's restore points
when starting up XP was to manually hide the Vista Partitions.