windows XP is the only microsoft operating sytem with a limit on half open tcp connections. The default number is 10, the justification is to "stop the spread of worms". not only has it failed at this but it also interferes with legitimate internet traffic. Torrents for example can demand around 200 half open tcp connections.
The patch from authorsite http://lvllord.de/
has been around for years and allows you to set it to somthing a bit more realistic like 600.
to see if your connection i s being adversely affected >start menu>run>eventvwr/system !warning TCP has reached the limit of concurrent etc