I need to give a folder access only to a single admin user, however this folder is inside a share readable to all admins. How to setup windows permission to give read/write to a single admin user and disable read/write to all others? I tried to "allow" access to the user and "deny" access to admins group, but seems that tha group deny won against a single user allow. But in this case i have no chance but set deny one by one to all other admin users... am i right?
DENY always takes precedence over allow. You could block inheritance on the folder and remove the entry that permits access. If the users are administrators, which you seem to imply, they can simply reset the permissions though.