Steps to Follow:
a) First of all , you have to download the torrent file with the extension .torrent which you wish to download...!
b). Then open up the browser page and go to http://torcache.net/ and post the torrent computer file that you have just downloaded and click on the cache button..,,!
c). This provides you with a new torrent computer file . You just have to copy the address (url) of the new torrent computer file from the newly opened up browser window..,,..!
d). Then visit to the web page http://www.torrific.com(Down these days) or http://zbigz.com/ (preferable) or http://torrent2exe.com/beta/and make an user account (in case you do not have one) and sign in to your Account. Then paste the address(url) of the new torrent acquired in step (c) and push the Get Button.,.,,...!
e) Now you will get the list of available Downloadable Files present in that torrent computer file. Then press on the begin bittorrent transmission button. This will provide full choice to download the desired file. Just press on any weblink and you can see the Internt download manager-IDM coming out for downloading the computer file.,.,.!!
Have a awesome dayy,,,,now enjoy downloading with IDM for donwloading torrents files as well…!!!

Alternatively:----
You can download directly from the http://www.extratorrent.com without using any  torrent client (but it would not be through IDM )...
Visit the above mentioned website search the content and download it as shown in the image below..