What is the best way to set up Dirty Mouse on someone's computer?

Wait for the victim to step away, run Dirty Mouse, and leave. The default 20-second interval is perfect -- frequent enough to be annoying but infrequent enough that the victim keeps thinking the problem might have fixed itself. For extra mischief, set a shorter interval so the freezes happen more often. When they start dismantling their mouse, you will know it is working.