db php question

I have a very crude script set up that I am using to keep track of IP addresses, MAC addresses, etc and it dumps into mysql. I am using a column called "id" which is my primary key and auto-increments. My question is that I want to make sure that I don't get duplicate IP addresses added into the database and right now it is a varchar field and anything can be put in there. If I change the column and make it my primary key will that prohibit duplicate entries? Is there a better way to do this? I am not a programmer either so I am having to hack my way through this. The second thing that I wanted to do was to be able to run a simple web form search for either ip addresses or computer name and return results. From what I have seen this seems pretty complex - any thoughts? thanks, DF