As I mentioned in other posts, suggestions for fine tuning for cross data access between distros would be appreciated
With respect to the data accessible across multiple ops, my recommendation is to set up one or more ext3 partitions to cover it. For example, I have dedicated partitions for:
All of the partitions are mounted via fstab in each of my available ops (4 linux and 1 windows at the moment
Once the partitions are established, just make sure you define them via the manual partition method in the install.
Also sounds like you might be ready for a dedicated GRUB partition. If interested, I've got a small paper that I've published on my website detailing the methodology (mine) for a dedicated GRUB.