Tired of that long lag under XP while your torrent spins up? Tired of your Web browser slowing to a crawl while you're downloading multiple torrents? If you're using Windows 7 or Vista, you probably don't know what I'm talking about. If you're an XP user, you do, and there's a quick and free cure: Half-open Limit Fix.
Basically, Half-Open Limit Fix increases the number of half connections (a requested, but not yet duplexed connection) by altering the Windows tcpip.sys file, which isn't editable with notepad or the like. XP's default number is 10, but upping this to as much as 100 allows other programs to open connections that your BitTorrent client might otherwise hog. Beyond 100 there seems to be little gain for most users.
Half-open Limit Fix couldn't be simpler to use. There's a field that shows your current half-open connection limit, and a field that you may type in your desired number. Click the "add to tcpip.sys" button and you're good to go. I noticed a large difference right off the bat. Half-open Limit Fix is a tiny download that offers big results on XP. Although the program supports Vista and 7, the higher default limit in those OSs makes it less useful on PCs running Vista or 7. If you're a torrent user running XP, though, get it.