There's nothing much you can do if your upload speed is 50KB/s, this speed is determined from your ISP connection. Two computer uploading at the same time on a single internet connection is actually going to make it slower.
BearShare is an example of what you are talking about but it require more than one single connect. You are downloading a single file off maybe 10 or more different people, You get a certain byte of file from one person and another byte of file from the others simultaneously and so on, than bearshare puts it together for you. This boost your download speed because you do not have to download off a single person who upload speed may be slow.