Well, until I read this piece, I thought I was going crazy. Strange words would appear in my email. Windows would close and open for no apparent reason. I was in Windows XP hell, but it appears that XP's speech recognition runs amok, and unless you bear the brunt of its phantom presence courtesy of your mic, you won't even know it's there. It's not quite obvious how to turn off the feature, but Microsoft support, according to this article, seems to know about the problem so, it might be more prevalent than most people imagine. Swearing at the computer doesn't do much expect send emails about forks.
Take a look at this article to get the skinny of XP's speech recognition problems.