Big Life Change: Going into Debt

I just signed my name at the bottom of a page promising me loans enough to keep me paying for the rest of my life. I'm going to grad school, have no debts and a good credit history. They wanted to loan me $42,000/year, and I bumped that back a good bit, because I know that I can live on substantially less than the $1,800/month they wanted to budget. The tuition is outrageous. I'm actually thinking that I might be able to have some leftover from my loans, and put it into the stock market where it could actually make more than the 7% interest I'll owe on it. It's worth a try.