Since your purposes here are strictly academic, you probably don't need to generate an overwhelming amount of traffic - just enough to demonstrate a grasp of the concept. With that said, I'd do two things:
- Download the following: http://sourceforge.net/projects/loic/ It's the tool that's most likely to be used for this kind of attack "in the wild", so you might as well use it.
- Install the same on whatever trash hardware you've got laying around. You really just enough hardware to make a noise on the network, so you're not going to need high-spec machines for this.
Note that these instances can be coordinated via IRC as Lucas Kauffman suggested (I think that feature is called "Hivemind" or something), if you want to go that far. Otherwise, just manually point them at your target and let 'em rip.