Recently I'm playing around with this useful program. I used to cap download and upload of Azureus in order to get reasonable latency to play online game. Now, it's not necessary anymore.

This program works by prioritizing ACK-packets. Perhaps this is the first program of its type (traffic shaper) in Windows. In linux, prioritizing ACK-packet can already be done.

Try it, and let me know the result
http://www.cfos.de/download/download_e.htm

edit: typo