AD Groups Permissions

Not sure if this is the right area, i'm a programmer not a network dude so...

If i have a group of people in AD, groupX that have permissions to some folders, can i add a local folder for write permissions to that group.

if i can, can i then add the public group to that group (groupX) and will the permissions trickle down to public even if public is more secure? i seem to remember something about depending on the groups you belong to in AD you have the least restrictive permissions of the set, so if i am in public (which everyone is) and i am in powerusers (which i am) then the power users group having less restrictions is the one that becomes my default so to speak. so if i create groupX to have special write permissions on the local machine (ie to program files/directoryx) and make the public group part of groupX groupX permissions will override public which does not have that particular permission.


hope that made some sense, i'm not eve sure now LOL...

TIA