himmm what i understand your dsl bandwidth is 512kb so when ever you upload a torrent the upload rate be 3kb right? okay i think it can be one of these problems
1- you may have spaywares. if that is the cause then you need anti-spayware program. you can see my post on http://blog.bitcomet.com/army3700/post_16745/
2- try to upload 1 torrent to see if it can take more than 3kb if yes then maybe because you share torrent connection in same trackers and that take allot of your bandwidth. for example let say two of sharing torrents (naruto + 50 cent ) has same tracker as( http://tracker.prq.to/announce ) when you share them all the peers trying to download from one server so the upload rate i think for 512kb is 128kb that divided into 2 then answer will be 64kb so the connected downloaders are taking from 64kb for each torrent so this will minimize the upload rate more and if there alot of downloaders this will make harder to upload torrents. and for me i have 1mb bandwidth but when i'm uploading the total uploads are from 5-16 kb :) and download rate are from 0-20kb so i have the same problem
3- it maybe because of the bitcomet program process try other torrent program to upload torrents this may work.
4- try to make the download and upload rate unlimited or no limit this could help to solve the problem.
5- the best thing try to use other torrent program to download torrents just to make sure if its working better or not then write to me if it works.
i just want to tell you i really dont know what the cause of this problem but this is what come up to my mind i hope i helped you 