Hi, Squeeze.
This one is going to be difficult for me to answer, as although I have the English US and English UK speech engines installed currently, it's difficult for me to tell if I'm using one or the other (since they're both English). So, here goes what I *think* you should do. First, go into the speech control panel and select, 'Advanced speech options' over on the left.
At the top of the, 'Speech Properties' screen, you'll have a dropdown list of speech engines to choose from. From there, you'll probably want to add a new profile (click New...). Then, train the speech profile in English (I'm assuming). At that point, you should be good to go.
Something to note is your English pronunciation, as it will affect the reliability of the speech engine. Something else to consider are some alternative speech engines (with several variations of English) that do not even require training. Those can be acquired here:
http://www.voiceattack.com/alternate Just a small engine to install and then the language of choice (also small). You'll then be able to choose the speech engine to use in VoiceAttack's options. Hope that helps some!
Are you also, 'Snoopy' on the Steam forum? Going to copy this over there as well.