So at this point are the accounts passworded or not? I think they may need to be to get this to work.
I have seen this issue before. Try with a fresh folder, not an entire drive, and share it by giving specific ownership permission to yet another user name on a fresh, passworded account, newly created on the connecting machine for test purposes. I dicked around with this for quite a while having the same issue but eventually I got it working.
Come to think of it I was connecting from an XP machine to a Vista machine. Not sure if I ever got the vista to vista connect worked out - I'll try and see.
edit: OK, I checked and vista to vista works, same username and password on the accounts and logged in as that user on both machines - I gave co-ownership permission in that pull down menu. If that doesn't work for you then I'm out of ideas.