OK, what you can do and can't do with FAT/VFAT WRT:Ownership and permissions
Owner/Group display is controlled by flags on the mount options and effect the whole mounted volume so regardless of what you chown/chgrp to if you check the file again you will probably find it's still root access. The g (group) and o (other) mask may also be set in the fstab if you really want (see man pages for this).
When you set permissions you can effect the x bit and the w bit, as the attributes entry in fat allows limited storage for rights (including read only) - x is stored in... don't know, probably the 'archive' bit on fat.
Notice though that when you change perms you can only change u+perm and that the g+perm options don't do anything. Notice also that setting u+perm changes g+perm and o+perm. This is becasue fat doesn't provide storage for multiple permission sets and has nothing like an ACL.
Regards,
Andy