Permissions for an entire PARTITION

[Richard Owlett <rowlett@cloud85.net>]

I'm in a multi-boot environment, multiple installs of Debian.
I want all install to have read/write/execute permissions.
The partition will effectively be serving as a common scratch pad 
in order to exchange information. There is organically a single 
user, [*ME*] and there is *NO* networking of any sort whatsoever.

How?
TIA