BitTorrent is largely dependent on others sharing the same file, so your speed is going to vary a lot, unless there are relatively large number of seeders. But your mileage will vary.
That being the case, there are other culprits that will rob you of decent download speeds. BitTorrent is based on sharing, so if you have your upload speed capped at a low rate, you will not be able to download at a very decent speed. The most likely culprits, however, are the settings on your router (or switch, but I will generically refer to both as a router).
If you haven't already, log into your router and check the port forwarding settings. If they are not forwarding the correct BitTorrent ports to your computer, it can greatly slow your transfer rates.
The following
guide [bittorrent.com] should give you all of the information you need to make sure your network is set up to allow you to download torrents. (Note: "firewall" in that document does not exclusively refer to a software-based firewall on your computer; it applies to routers as well as both will often have similar settings and options).
Good luck.
