After years of struggle with Tcp/Ip patches, Microsoft finally remove the half-open connection limit.
Since Windows XP SP2 Microsoft limited the maximum half-open connections to 10 only. this limitation have caused many file-sharing applications to slow-down their download rate, and Event-id 4226 has flooded the system event log.
In Vista SP2 this limitation is finally gone! you can read more about it in this KB969710 Article
If you still wish to keep the limitation running (for any reason I can't even think of..) then use this registry tweak:
Those of you who still works on older versions of Windows (Vista/SP1, XP-SP2/SP3) can use this Universal TCP/IP Patcher from Deepxw. Another fine patcher from Half-Open.com
UPDATE: The same as Vista SP2 update, so does Windows 7 not having the limit for the half-open connections.