I admit, the reason I don't know the answer is that I've never managed to pull this one off, but one of my friends put power steering fluid in the oil tank. Anyone who knows the best course of action in this situation? Keeping in mind that not only does he not know how to change his own oil (Given that, and given that he knew that, I REALLY don't see what he was planning to accomplish) but as far as car knowledge goes he makes me look quite knowledgable.

I once accidently put power steering fluid instead of brake oil. I was told that it wasn't going to harm it.

I don't really know if this too will be ok. I mean, I am not a mechanic either, but it is basically oil, it's not like putting water. I would call a mechanic and ask.

Do you mean power steering fluid in the crankcase?
If so, I would change the oil again and put some kind of treatment in to remove the power steering fluid completely (if possible). Then change the oil again.