the new facebook Groups only alow admin to post on walls and there is no way to message individuals..

 given below is a example that just demonstrate how i done to my group 

 So The Group URL Of This Group look like one link below..

http://www.facebook.com/home.php?sk=group_171220776264897
 Remove Everything except The Numbers At The Last.. that number may vary for ur group....

So Here Is What You Got

Now Type This In The Address Bar:
http://www.facebook.com/inbox/?compose&oid=your group unique id 
  
So Here Is The URL updated 

For This URL you can message All Members!!

NOTE: You Will Need To Be The Admin To Be Able To Do This!!!!
when you go to the link you can seea a image like one given belo so You can compose your message
and post to your friends... i dont no how much time we can able to do this.