Is there an option on Facebook to prevent some of the people ,that I already am friend with,from watching who all my other fb friends are?and if yes how can I enable it? Thank you

Privacy Settings > Profile Information

Did you click on "Customize"?

Privacy Settings > Profile Information I don't mean to hide everything just the rest of my friends

With the Customize feature you can select who does not get to see the type of info you selected.

With the Customize feature you can select who does not get to see the type of info you selected. where exactly is the friend option so I can customize it?

I just re-read your question, I'm sorry I misunderstoof what you were asking.
It looks like you cannot stop friends from seeing your list of friends in this new Facebook and some people are mad about it: how do you stop people seeing your friends on VIEW FRIENDS??????? | Facebook (http://www.facebook.com/topic.php?uid=2305272732&topic=4297#topic_top)

Try this: Now, Facebook Lets Users Hide Friends From People Who Are Not Logged In (http://www.insidefacebook.com/2009/12/10/now-facebook-lets-users-hide-friends-from-people-who-are-not-logged-in/)