Well, since i unsucceesfully tried to find a solution on several forums, i realized that this is a real taboo thing in networking comunity.
Somebody tells it's not possible in xpp, somebody claims it is, and then nothing, no explanation, no instructions on how to - nothing.
Maybe this forum has someone who knows:
I have a p2p lan with all comps on xpp and simple file sharing.
Works all right.
I disabled SFS on one of the machines in order to protect just one of its shared folders in such a way that only a certain network users can access it.
I successfully set (ntfs) permissions, so it works fine as well.
The only (but big) problem is that i want the mentioned comp prompts for user password whenever some of those permited remote lan users tries to access the protected folder, nevertheless it already has the permission to access the folder. I don't want those users go in automatically but through the login prompt.
This is because i don't want somebody else to sit down by permited machine and access the folder automatically.
I simply cannot believe this is not possible in XP Pro.
If someone solve this issue i'll propose him/her for the Nobel Prize for Networking.