Sure. You might be surprised to learn that the load on an average home router is probably pretty low most of the time. Do the math: even downloading at maximum DSL or cable router speed (even if it were small packet sizes, which in higher loads is not usually the case) is just not a significant load on a modern CPU these days.
Scripting loads is easy. I have a script that I bang against Comcast sometimes when I doubt their last mile link to my home. It simply uses wget (or try curl) to download a file of reasonable size repeatedly and records the download statistics (time and/or data rate) of the transfers. Just find a .pdf or other file of the size you need from around the net somewhere, or use a busy website with lots of content. Just avoid the little guys who might have to pay for that bandwidth you are consuming in your test. Better yet, Amazon S3 storage (and transfer bandwidth) is very cheap these days and easy to use. You could put some files of your own choosing up there, and download those repeatedly for your test environment instead of stealing bandwidth from someone else! ;)
Never played with any torrent clients, so I can't help you there, but I bet there are some you can script.
Also, you might check out netperf. I don't know the status of that project, but I've used it in the past to generate very high network loads. Google for it.
Have fun and good luck!
-Chris
