Will Information Science hold me back? I would still have a chance to do my masters on AI or anything without a "Computer Science" UG degree right?

Universities in the US will not differentiate between Information Science and Computer Science. Rather, they tend to check each individual subject you've studied or will study in your UG degree. As far as studying in a particular field goes, it depends on not just the subjects you've studied, but also the amount of extra work you've put in learning about subjects NOT present in your regular curriculum. If the university feels that you have the capacity to handle the present course structure, they'll give you an admit right away. If they don't, they sometimes ask you to take up a few bridge courses, where you'll have to take up some extra courses not present in your curriculum. Without completing the bridge courses, you won't be allowed to take up any other courses. In the end, It'll boil down to what you prioritize - the curriculum of the course or the reputation of the university. So rest assured. You will not be subjected to "discrimination" just because you have a degree in Information Science. I can tell this for a fact because I also have a degree in Information Science, and I'm leaving for the US this August to do my Masters in Software Engineering. (though it isn't AI/HCI as you asked, I think you'll understand how this works)

Yes you can. In fact you can do masters in any field in USA (Maybe in other countries as well I'm not sure). Yes you can choose to do masters in any department. You should have a valid reasons for choosing particular department. Checkout http://happyschoolsblog.com or http://msinus.com and http://stupidsid.com etc. For more information.