Windws XP SP2 introduces a few new twists to TCP/IP in order to babysit users and “reduce the threat” of worms spreading fast without control. In one such attempt, the devs seem to have limited the number of possible TCP connection attempts per second to 10 (from unlimited in SP1). This argumentative feature can possibly affect server and P2P programs that need to open many outbound connections at the same time.

My download and upload speed on Torrent and P2P has slowed down tremendously after updating to Windows XP Service Pack 2.
The file TCPIP.SYS needs to be modified in order to have more TCP connections.
Unfortunately there exists no REG-key which could easily be set (would be so nice and easy, right? *smile*). The file TCPIP.SYS in the directory C:\WINDOWS\SYSTEM32\DRIVERS and C:\WINDOWS\SERVICEPACKFILES\I386 has to be changed (system dependend eventually in C:\WINDOWS\SYSTEM32\DLLCACHE, too).
Markus Goslar from LvlLord has created a patch called Event ID 4226 Patcher (4226 fix).
It automatically patches your TCPIP.SYS to allow TCP connection from 10 to 50 by default. You can specify the amount of TCP connection attempts you want as well.

[ Download EventID 4226 Patcher Version 2.23d (english) ]

To restore your TCP connection attempts if you’ve patched your TCPIP.SYS, just run the patcher again, and it will prompt you if you’d like to restore your TCP connection to 10.