Flutterby™! : Network degrader?

While I'm asking about silly gadgets: I've got a few fixed IP addresses on my DSL. A friend of mine, who can only get Comcast at his house, stashed a machine on my network. He runs a personal web site and some mail off of it.

My internet performance has been sluggish recently. I'd love a little device I could plug in between his machine and the router that let me dial down his bandwidth, maybe just by simulating a bunch of extra traffic on the ethernet port on his machine. That way I could see if that machine is the source of my slowdown, without blowing his mail all together.

I guess the real issue is that I've got this little consumery DSL modem/router, and what I really want is a real router.