Windows XP Service Pack 2 Limits Outgoing TCP Connections
In other words, if you are using any filesharing software, you should limit the number of sockets it will try to use at any given time.
Let's say that you are set to 20. We don't know what the limit is, but let's say that it's set to 8.
Your filesharing app will try to create 20 connections at the same time. However, only the first 8 will actually be created. The remaining 12 will be placed in a queue that will slowly be emptied based off of socket closures and connection successes.
However, mind you, this is not an application-specific limit. THIS IS A SYSTEM LIMIT. That means that any TCP connections that any other applications try to create will also go into the queue. However, most applications do not support the "queued" sockets. Internet Explorer, for example, will immediately pop up the "DNS Error" page if your unqueued sockets are full.