Unfortunately, no, you can't limit it to 0.5 threads.
You can set a priority through task manager, but the CPU will still "max out."
It's unlikely you'll burn anything up. I have no idea if you're running your computer out of a toaster oven or have it dangling from strings in a closet, so there's no way I can guarantee one way or another. If it's an older, general use computer you may want to make sure all of the fans are clear and hit it with some Duster or compressed air to make sure you have good ventilation (you should do this, anyway, even if you only use the thing for Solitaire).
.... I'll just say it's unlikely.
