Advanced bittorrent clients offer selecting the files we need to download. But thats a feature i've seen only on Windows based clients. (sorry folks.. havn't tried azureus.. if at all it does support. my configuration does not support this heavy app.). i was just wondering... is it possible that we manually edit .torrent files and/or select the files to be downloaded...( :-/ . i am not sure if we actually can edit a torrent file..pls enlighten me). Any tool that helps in doing so? or any other way to get this objective on linux..??

The torrent file is only a link with some extra information like file size and whanot. For whole folders and all, it doesn't work to try and edit it. It wouldnt work within zips or pretty much anytime, except on rare multifile with no folder torrent links, but as those are bad ettiquette to post, pretty much no.

ABC has a Linux Torrent client in beta, it works for doing what you want.
Azureus will do it, but as you said it is a heavy resource, and current versions of it actually have some issues with some routers and highspeed modems, causing them to reboot or become unstable and lose connection. It is rare, but it happens on my modem.

A google search will pull up tons of other clients that meet your needs, like TorrentFlux, even whole directories of them like on source forge so you can look for ones you need.