DirectoryInfo dirInfo = new DirectoryInfo(@"C:\Temp");
// Get a DirectorySecurity object that represents the current security settings.
DirectorySecurity dSecurity = dirInfo.GetAccessControl()
;
// Add the FileSystemAccessRule to the security settings.
dSecurity.AddAccessRule(ne
w FileSystemAccessRule(@"Adm
inistrator
\vinod",
FileSystemRights.Delete,
AccessControlType.Deny));
// Set the new access settings.
dirInfo.SetAccessControl(d
Security);
Or you may refer this page
http://www.codeproject.com/KB/dotnet/adduseracetofile.aspx