Windows XP SP2 introduced a limit on concurrent half-open TCP/IP connections that can be a problem in using P2P apps like eMule, BitTorrent.
http://forum.emule-project.net/lofiversion/index.php/t56016.html describes the general method of dealing with this.
However, there is at least one other version of tcpip.sys that is different. I believe this is part of a more recent windows update. The same hack can be applied but in two different places.
First check if your tcpip.sys has a size of 359,808. If so apply this patch:
Modify tcpip.sys offset 0x130 from C8 27 06 00 to BC 28 06 00
Modify tcpip.sys offset 0x0004f5a2 from 0A 00 00 00 to FE FF FF 00
An automated fix for this is found in http://www.lvllord.de/
I will post a more general description of what we're modifying later in this blog.