Try a different client - e.g. muTorrent or Azureus.
However, many ISPs now limit bit torrent traffic to about 50 or 100 kB/s regardless of your connection speed or download limit. This 'traffic shaping' is becoming more and more common, as ISPs try and claim 'unlimited bandwidth' (by slowing down torrents, they reduce the impact big downloaders have on other customers).
One option is to activate 'encryption' in your bit torrent client (don't know if bit comet does this, but muTorrent and Azzy do). Encryption will prevent your ISPs systems from recognising your downloads as bit torrent traffic, and so they by pass the limiter. However, router manufacturers are now introducing routers that can detect encrypted torrents, and apply the same limits.