Hi there. I am with a cable company ntl and i was getting slow down load speeds i kept complaining to them they told me it was my router( LInksys WRT54G). that was giving me the problem (ya right i thought) so i went to linksys website and did a firmware upgrade and low and behold it was the router that was slowing me down.
You may have done this already as i am no expert but these guys on this site have helped me