Both Bitcomet and uTorrent (and probably other clients) limit half-open tcp connections by default. This means even if you hack the max half-open tcp connections in windows xp, your speed will still be limited. So this is what you need to do:
1. Hack the max half-open TCP connections
If you’re on XP sp2, your TCP connections are limited to a maximum of 10. This seriously hurts your downloading speed because it wont let you connect to a high amount of ip numbers. It is supposed to slow down viruses because their spreading strategy is to connect to a high amount of ip numbers, but it also cripples your torrent downloads.
A nice way to fix this is to download this patch, it allows you to set the maximum allowed connections to any number you want. Any number between 50 and 100 is ok (more is NOT always better).
2. Configure your torrent client to allow 50-100 max half-open TCP connections
uTorrent: Options > Preferences > Advanced options > net.max_halfopen
Bitcomet: Options > Preferences > Connection > max half-open TCP
Now you’re ready to go…
A third point of interest is that some “windows updates” revert your tweaked tcp connections back to 10. So it’s wise to check this every now and then. You can check this by going to (in windows xp) Start > Control Panel > Administrative Tools > Event Viewer > System… Look for event 4226 (sort by event).
If there are a lot of daily occurrences it’s likely that the max amount of half-open tcp connections was set back to 10. Or you’re infected with some nasty spyware…
If you’re done, you might want to try the torrent settings optimizer to check if all setting are correct