Note that this would often be an unpaid research experience, either as a volunteer or as part of a thesis or project course. In some cases, I may have special funding for undergraduate researchers who are US citizens or residents - let me know if this applies to you.
Also, be advised that I expect a significant time commitment on your side, plus a very strong academic background and motivation. In particular, I am looking for students with strong programming and algorithms skills, and preferably with some background in web search, data mining, or machine learning. If you are willing to invest the effort, participation in research activities can be a very valuable preparation for the job market or graduate school. But you should be significantly above average in your grades - if you are struggling with your classes, it is better to focus on those.
If you are a prospective MS student, then it is very unlikely that I would be able to offer you financial support, so there is little need to contact me before you have been admitted. After you arrive on campus, we can talk - but see above and below.
Feel free to talk to me about possible research after you arrive on campus, but be aware that most likely this would be an unpaid research experience, at least for the first semester or so. Also, in most cases I would recommend talking to me after you have been on campus for 2-3 months - once you have adapted to the new environment and know how much time you need for coursework, and how much time you have for possible research.