I am having the same problem however its my brothers computer running kazaa that sucks up all the bandwidth.
My thoughts on how to limit the bandwidth are to install a different packer scheduler on the router to give my computer priority on sending packets instead of FIFO which is IIRC the default scheduler. I haven't finished compiling all the packages on my router as yet though so beyond the thoughts, not much has happened so I cannot tell you if it'll actually would work.
Once I get it done, I will help if you need it. If you find out some other way to limit the bandwidth please do tell.