Use NFS - it lets you have groups and everything working as for a local file system.
Or, use samba :-) the "unix extensions" options work well for unix<->unix connections - understands permissions properly (plus the possibility of mungung them to meet your requirements)
I'm not aware of any successful generic scheme for sharing directories that is applicable for GUI users :-( I suspect what's needed is the "sticky-bit = enforced group ownership" on diretcories, but I suspect these aren't in ext2/ext3. Possibly xfs or Reiser? I *know* I've used them on some unix versions, but I can't rememebr which ones.
-jim
