It's still possible to sign up for classes, it's rolling admission.
It looks good on your application. I work for the particular office that takes care of the applications, and usually what we tell people who ask that question is that it doesn't hurt to mention it on any college application because it means you went through a college type setting program (since most of these courses are taught pretty rigorously and are instructed by either professors or grad students) it means that you can handle a college-type education. If you successfully complete the course, you receive a certificate of completion, which you can photo-copy and put with your college applications.
You have to apply to these programs. There's an application, you need a teacher's rec, and an official transcript. There's also a application fee of $60 (which will soon turn to 90 dollars...I think) Again, its rolling admission, but popular classes fill up and get wait-listed and you're not guaranteed a spot in the classes you pick.
The website has TONS of information (
Brown University Summer & Continuing Studies) read up and if you have any questions that are not answered, call 401-863-7900 and the lovely ladies who answer your call will be happy to help.