vista share incompatible with win 7

Hi,

I have 3 computers in workgroup,
* 1 vista home edition(let's name it c1),
* 2 win 7. home edition (c2 and c3) .
* all computers have been set in ^the same workgroup (named WORKGROUP).
* all computers can ping each other and appear in network neibourghood

The aim is to allow c2 to access only some shares and c3 to access only some
other shares.

On c2, I created user2 / password user2
On c3, I created user3 / password user3
On c1, I created 3 users:
user1/password user1
user2/password user2
user3/password user3

On win 7, network profiles are "residential workgroup".

On c1 (vista), I create a network share named test, on a folder, all
computers can see it and read contents. (So far so good, means fw and
network allow sharing).
(File permissions are "everybody has read/write access")

Then I tried to set permissions on the share on c1 (server), and this is
where I don't understand the logic.
* if I add to share restrictions to user2 (refuse all): user2 can still
access the share (perhaps because of "everybody", but it is strange).
* if I remove permissions "everybody can read/write the share" , and add
user2 can access share (giving full control), nobody can read (nor user2 nor
user3). Why Why Why?
* if I add permissions on user3, user2 and user3 can then access share.

So I was not able to tell that a share could only be accessed by only one of
the users.

But I have another problem (cause or consequence): if I set share
permissions to "full control for user2": from c2, logged on as user2
(password user2), share is shown but no access. In command line:
* net use x: \\c1\test
* dir x:
=> access denied
* net use x: /delete
* net use \\c1\test /delete
* net user x: \\c1\test user1 /USER:user1
* dir x: works
* whoami : c2\user2

So it seems that login username/password of win7 is not given automatically
to vista when accessing a share. Why? Due to "residential workgroup"
profile?
Any help welcome.

Regards,
Alain