Generally speaking, most of the big banks have some sort of matching process after offers are handed out. They bring you up to NY for a "sell day" where you interact with the different groups and show your love for them. Then, you submit a top 3 or something like that, and the groups come up with their top 3, and people get placed according to need. Of course, it differs for each bank. Some have a rotational system so you choose one or two and one or two are assigned to you based on need and aptitude. Other banks are generalist and you basically just go into a pool.
If you have strong interest in a particular group, you can make it known during the recruiting process, but this can be extremely risky. They might view you as inflexible, and beyond that the group you're interested in may not be hiring. The best thing to do is probably to let banks know that you are interested in certain areas (at least 2 or 3), but say that you are willing to consider anything. That way they know you've given it some thought, but won't be a problem. Unless you're absolutely fixated on a particular group, I think the smartest thing to do is to use the matching process to find people you like to work with and mentors that will stand up for you during the summer and beyond. To me, that's a lot more important that trying to force yourself into a particular group.