<p>Yes, MIT students can UROP in Harvard labs – my lab (Harvard/Mass General) has an MIT student in it now, and a few of my friends did summer work in labs at Harvard Medical School. (EDIT: Keep in mind, though, that doing research somewhere other than MIT’s campus tends to cut into the amount of time you can do research each week – if you have a 30-minute commute to your lab, you’re not going to get as much done as you would if your lab were within walking distance of your dorm.)</p>
<p>And plenty of people UROP as first semester freshmen, although plenty choose to wait until second semester, the summer, or sophomore year.</p>