I can't confirm it for 8600GT, but I have a 9500GT with the same connectors, and it will only do 2 at a time.
You could run one of those USB video adapters, they're available for cheap used, and it's workable for basic tasks (full screen video/gaming are obviously nearly impossible on those devices, but office/web/email/etc are fine).
Of course, once you spend more than a few bucks, you could actually look at something like a 5670, which works just fine for that.