Try using a much higher port, like 64049. Make sure that it's your listening port & also allow that port through the XP firewall.

I don't know if this will help at all but check the link below & see if any info there is useful.
http://text.dslreports.com/faq/eff/6_5360


There have been some suggestions of MTS throttling p2p bandwidth, it might be worth checking with them to find out their policy re p2p use.