^ Ok, I just wrote a huge message answering this question and it all got deleted because my internet went out when I tried to post it.
In any case, I only know of 2 people who are actually getting paid. One as a clerk for a judge and another with a "big law" firm. There are probably a few others that I don't know about, but I do know that over 150 people are doing the summer internship thing for class credit. AND, I am sure most of them are 1Ls. The thing is that "big law" firms didn't hire many 1L summer associates to begin with, and with the down turn in the economy, some have scratched the 1L associates all together or gone down to only 1 or 2. You don't have enough credits to get your temporary license to practice law until after your 2L year, so you are pretty limited in what you can actually do after your 1L year.
While you don't get paid for doing a judicial internship/clerkship most of the time, you can get up to four hours of class credit, it looks AWESOME on your resume and firms love to see it, and you get to learn all of the ins and outs of the legal system. It is really an amazing opportunity and invaluable experience. If you are really strapped for cash during the summer, you can take out summer loans and financial aid if you are enrolled in the externship program.
On-campus interviewing (OCI) takes place in August-September of your 2L year. A ton of "big law" firms come and conduct interviews for 10 week summer associate positions for the summer after your 2L year. Like I said, you get your temporary license to practice law at the end of your 2L year so you are actually really useful to them by then lol. Generally, at the end of the 10 weeks the firm will offer you a job that will begin after you have finished your 3L year and taken the bar. I also know people who have done clinics (domestic violence, civil litigation, etc.) during their 3L year and represented real clients.
Anyways, hope that somewhat answers your question.
P.S. I am completely in love with your avatar (Riggins from Friday night lights... *sigh*)