But this thread is so wrong in the advice that they give. Since it was so rusted, it was relatively easy to cut the old one out with a dremel tool and remove it. This leaves the unrusted PVC drain pipe about 7mm off the floor. Then, if you go through the aisles of Home Depot (I couldn't find it on their online store - strange), you can find a two piece closet flange which you can just slip underneath the PVC pipe. The two pieces are joined together using the same uprights that you attach the toilet to. The only downside for my repair is that only two of the six holes in the replacement flange were in spots that the old one wasn't - and the other ones were basically unable to tigthen to the screw. I bet some kind of compound could be added to the holes where the screws were and give some bite to the screws.
