Download ABC Bittorrent (good P2P bittorrent client, I use it)
http://pingpong-abc.sourceforge.net/download.php
Action > Global Upload Setting. Then tweak the preferences in that. I think the smallest you can set your upload per download is 2 or 3 KBps. Though if you're downloading more than 1 file the limit is seperate so say for example if you've set it to 2KBps limit and you're downloading 2 files then you'll be uploading 4KBps.