How does P2P software like Limewire works?

Question

I mean if i m downloading a file from a user and If he goes offline , will be downloading still continue?

Answer 1

It depends. If someone else has a complete copy, you'll get it. I dumped limewire (it runs the Gnutella Network) for BitTorrent ages ago so I working on memory here.
Usually you'll see several peers listed in the download pane. If only one of them is complete and goes offline, your screwed. Gnutella, Gnutella2, FastTrack (Kazaa) and the like use sequential downloading. The files starts at the downloading at the beginning and goes to the end of the file. This allows you to preview the file with VLC media player, for example, but leaves no option for uncompleted downloads if the source(s) go off-line except to wait for a source or sources to come back online..
I wont even get into the huge amount of fakes the RIAA and partners have flooded these networks with or the incredible amount of malware present.
Check the first link below. It's a limewire FAQ. Look for the question: Why do I keep getting "Need More Sources"? and look at answer 2. This is why, along with fakes and malware, I dumped these older clients for BT and NewsGroups ages ago.
As an alternative, try bittorrent. It uses a different system that allows for redundancy. The chunks are spread across the network (swarm) randomly. This means that the odds are good that someone will have the chunk you need once the torrent has been fully seeded.