Dear Ms. Fletcher,
You don't need to punish your daughter - this behavior is within the normal spectrum. All you need to do is talk with your daughter about the inappropriateness of such behavior (I'm assuming, by the nature of your question, that the kissing was of a type that simulated adults' kissing). It's a time to educate your daughter via guidance and advice, not a time to punish her.
My 5 yr old son wanted to give me "sloppy" kisses (on the mouth with lips open)that a 9 yr old told him about at the baby sitters. Now while I like kisses I did not want that kind. It took me nearly a week to get him to go back to the normal mother/son kind.
Kids are going to experiment and they are so influenced by TV, peers, and older kids. Kids at this age do not know that they are doing something socially incorrect and need guidance not punishment. When I saw someone at the mall or restaurant exhibiting correct behavior I always pointed it out and used the situation to explain proper behavior bringing in a prior "bad" behavior my son was doing. My son used to stand up in his seat, talk loudly, etc. in restaurants. I started saying "Do you see anyone else doing this? Have you ever seen me and Daddy do this?" It finally got through to him and he does much better now.
I used to punish for everything but teaching correct behavior and giving specific praise for positive behavior works so much better. And cuts down on the tantrums and arguing (on both sides!).