Hmm I actually heard of a little piece of software that tells the computer your mouse is always moving (without actually moving your mouse) so that it won't go to sleep. I'll try to find where it was real quick...

Also, couldn't you just disable your computer from going to sleep at all? Right-click on your desktop, go to Personalize, (on windows 7 it might just have a Screen Saver option when you right click instead; I can't remember) and there should be an option to set it to never sleep. If that doesn't work let me know and I think there's an option in Power Settings...

Or did you just want it to not sleep when you're streaming? That would be a bit more tricky...

I can't find that mouse moving program, but this one will work just as well: Give your computer insomnia [Free tool and source code to temporarily prevent a machine from going to sleep!] - Delay's Blog - Site Home - MSDN Blogs just scroll down a bit for the download.

Based on the user comments at the bottom (and the fact that seems like it's a pretty universal Windows controller) I'm pretty confident it will.