Not all direct loans have subsidized interest. Most of my loans are of the unsubsidized type, and while not due while in school, accrued interest from the date of issue. Some of my loan money is subsidized, and is not accruing interest while in deferment.
The first chunk of my loans, issued pre-Fall 2006, are at ~1.8% and is a variable rate. My loans issued Fall 2006 and onwards are at 6 and change. My only complaint is that they refuse to let me pay back the higher interest loan first, telling me that federal law prohibits it.
Loans for graduate school are higher, my wife has graduate PLUS loans at the 8.5%.
2 years in the Peace Corps will not forgive any of your loans, it will just get you a two year deferment. Those PLUS loans of the OP are going to sit and accrue interest at 8.5% for two years. The $6,000 "resettlement" cash PC gives you when you return won't cover the interest on his loans. Not withstanding any other benefits (increased employability, personal growth, ect), the PC is a poor economic decision for recent graduates with unsubsidized loans.