It depends on how many people are seeding the file. Does LW show that you're downloading the torrent from lots of hosts? Your download speed can also depend on your own seeding of the file that you're downloading. Sometimes you won't see good download speeds if your own upload speed is very low. And sometimes it can be a matter of waiting...I've had torrents stuck at 2 or 3 KB/s for ages & then just take off!

LW's torrent support isn't the best yet & I think some sites may have banned LW, so you may not be able to download from as many people as if you were using another torrent client. Try searching on a few different torrent sites & see whether a different version of the file goes any better.

You can also make sure that your LW is set up for optimum performance. Check out this thread(the first few posts by murasame).
A few things to consider while configuring Limewire for optimal performance...