wizpatch,
If you are talking about what I think you are talking about ISD is basically the "early selection" of NROTC. I think to be eligible you'll need high Math and Verbal scores ( I had a 32 English and 30 Math ) and a great high school GPA. Basically, you'll have to talk to your NROTC liason and tell him you're interested in getting an ISD spot. Each region has a limited number of these spots so best bet is to get in early. I received my early selection in september and to get selected you will have to interview with the Commander of your region. (Make sure you're on time, my interviewer intentionally never called me to see if I would take the initiative to call him and be on time. He said afterwards many people don't ever call him and never get their early select). Benefits of the program are that you know you have the scholarship, you don't have to go before the boards, and since you get the spot early, you are almost guaranteed your school of choice. Let me stress again this is the most competitive way to get an NROTC scholarship and I was told it was on par with being selected for the academy. Hope this helps! Good luck.