Recommendations for a BotNet/DDoS Penetration Tester

I'm doing a project for my school in which I'm supposed to write a program to disrupt the bot master, in a bot net based DDoS attack. Would any of you know of any good free software which is able to run on windows for a local DDoS attack? I haven't got the time to learn a new OS/Programming language to initiate the attack in which to test my disruption program on.

P.S. A GUI program would be nice, if not a .c type cmd program works too.